Just picked up a Winchester 1873 and holy cow is the front sight hard to see. Any options out there? This is a 20" carbine so the front sight is not dovetailed into the barrel.

Several options........

The simplest is to apply some model paint to the sight.
You can easily experiment with colors like White, Fluorescent Red, or Lime Green, which is the most visible color under all light conditions.
The Red and Lime Green show up even better if you first apply a coat of Gloss White, allow to thoroughly dry, then apply the main color.  The Gloss White undercoat makes the top coat "pop" much better.
The paint is reasonably durable, easy to remove and change, or reapply.
Best, it doesn't require a permanent alteration of the gun so you can put it back into factory condition.

Second option.... Soft solder or even epoxy a piece of brass to the rear of the sight blade.  If you have the skills you can cut a notch out of the sight and solder the brass into the notch for a more "factory" look.
White or Bright Orange plastic also works with a good epoxy.

This requires gunsmith skills, but cut the sight down and mount a "Fire Sight" optical fiber insert to the blade.

The paint might work but the problem is how thin the front sight is. It's a thin piece of brass pinned into a block sticking up from the barrel.

Sounds like an 1895 front sight. If so your only options are to order one from XS (they may be discontinued) or get some brass flat stock and cut/file your own.

Another idea is small brass tubing from an RC hobby shop ( like fuel tank tubing) cut a thin lengthwise slot, pinch it to add tension and slip that over the front sight.

I understand your complaint.  I've had four of the newer Winchester lever rifles, and the stock brass beads on all of them have been hard to see.  I put a Marbles fiber optic front sight on my 1886 Deluxe along with a bullseye rear sight, and it is a world of difference.

What does the base of your front sight housing look like?  Almost all of them are dovetailed, so I am curious how they have the sight in there?

Since the rear sight should have a dovetail, you could try grabbing one of the Marble bullseye sights as it'll make your sight picture 10 times better even without changing the front sight.

Here is the front sight. It's a very thin piece of brass sandwiched into a slot. No bead at all. The base is definitely not dovetailed into the barrel.

Easy peasy.  Get a piece of brass the width you desire your new front sight.  Slim it down uniformly to the thickness of the existing sight for a tab that will be  inserted into the front sight base. Insert new blade into front sight base and bam...  Wider front sight.  e.g. Make something roughly like a "T" where the bottom of the T is the thickness of the existing blade and width of the top of the T is the width you want the sight.

Sorry, I thought you had a 1873 that used a steel one-piece front sight like my old Uberti '73 Carbine.

Options are to do as above and make a wider sight that is thinned on the bottom to fit the base.
The other option is to file the base to widen it so you can use a wider piece of brass.

The "best" way is to make a new brass blade, because a primary Rule of Gunsmithing is to work on the part that's cheapest-easiest to replace if something goes wrong.
Botch up the base and you're screwed.  
Botch up a new brass blade and you just start over, no harm, no foul, more brass plate is cheap and easy to get.

Unless you have access to a milling machine or someone who does, a simply manufacturing method is to lock the brass in a vise with even jaws and use a safe edge file to file the exposed sides to the required thickness.
File on both sides with the safe edge on the vise jaws.
File the bottom to fit before doing any shaping of the sight.  If/when the first attempt doesn't work out you won't have wasted time shaping the blade portion.

If you're planning on doing any filing with the new blade in the barrel, tape the dickens out of the barrel all around the base.
This will save you if you make a slip.  Tape is cheap....use plenty.

I suppose I could always have a dovetail cut into the barrel and add a bead front sight.

I wonder if a Marble's tang sight would make any difference. I have noticed that the notch in the ladder-style rear is pretty shallow and narrow. Hmmm...

Yes, a marble sight would probably make a difference.  But again, a safe sided needle file and 15 minutes of your time and the notch can be made to a custom width that suits your eyesight.  My preference is about one front sight blade width of light on each side of the front sight when viewed through the rear notch.  Again very easy.   As DFeriswheel said, use lots of tape all around the sight where you might have even the slightest risk of slipping with the file.

His rifle came equipped with what is known as a "National Match" front sight.  

My question is,... why is it NOT black?

Spray it with sight black or use a carbide smoker to blacken it.  Once blackened, it may work just fine.

Yeah, I'm actually wondering now if the problem is the rear sight. The notch is TINY: 0.036" by my digital calipers. I painted the front sight neon orange and I'm going to blacken the rear a little and see how it shoots before making any changes. I have a feeling I'll end up going with a Marble's flat top sporting rear, which should have a bigger notch, or a Marble's tang mounted peep.

Rather that "hoping" spend 15 minutes with a set of Harbor freight needle files and make it exactly like your eyes want.  Don't forget the tape and cold blue.  I'm not trying to harp on you but this is so simple.  Looking at your shop in the background of the photo you posted, you probably already have the tools needed and if you don't no better excuse to remedy the situation.

As I mentioned in my other post, I'd try replacing the rear sight with a Marbles bullseye sight.  The sight picture is so much better.  My 1886 came with the buckhorn rear sight and like yours, the notch is super small and it;s hard to pick things up.

Here's the sight picture on my 1886 with the bullseye sight.  I couldn't get the camera to focus on the front sight but you get the idea:

You overestimate my skills, sir. Honestly, I'm not even sure I have a file thin enough to get in that rear notch. I know this thing isn't exactly a collector's item, but I'd like to keep the original parts... original.

Yeah, I really like the look of that. I ordered one from Midway, along with a Marble's flat top rear to see which one works better for me.

Now THIS is more like it! Can't wait to get it to the outdoor range and see what it can do at 50 and 100.

Very nice!  Did you paint it or get a whole new insert?

Testors white enamel, and then fluorescent orange over the top. Just have to remove the paint if I want to return it to original condition.

Now I just need to figure out something with the butt. It really slides around on my shoulder. I've read that you can glue a piece of rough-out leather to the butt plate. Not sure I want to go that route. Not sure I like the idea of a butt cuff either...

Tang is the route I went with my 73, too. It made a world of difference.

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