I'm looking for a replica of the U.S. Mark 1 Trench Knife (I believe that's the correct name) for a friend for Xmas. Does anyone have any recommendations on which brands are good or where to get one?

There's only one current actual replica available as far as I know, and frankly it's absolute junk.
These are made in either Taiwan or China.
The handle is rough cast brass and is shaped nothing at all like the original Mark One or even the better quality Japanese made versions made in the 70's and 80's.  It's way too thick in places like the guard and the knuckles, and the shape is way off of the original or Japanese replicas.
It's serious junk.

There are several other Mark One "type" knives, but these have blades that are totally unlike the original and are even worse junk.
Some of the replicas are being made with cast zinc handles, and some are modified like WWII issued Mark One knives that had the sides of the round guard cut off.  All still junk.

The "scabbards" of all the replicas are seriously horrible trash.
These are made of cheap, thin steel, "sort of" pressed together.  it's not unusual to open the box and find it fallen apart into the two halves.
The belt clips on the back are spot welded on. You can easily break them off with a good tug.
In no case can these be used as an actual scabbard, and some sellers sell them as "blade covers", which is all they really are.
Some of the current knives may come with leather sheaths instead of the metal one.

The blades are much better.
All the replicas I've seen over the years have stainless steel blades which are thinner than an original Mark One.
The new replicas are much better shaped and made then the older replicas or even the original Mark One but this doesn't make up for the really crappy handle.
The nut that holds the blade in the handle is way too sharp and unlike the original or Japanese replicas.  

Here's a picture of the current junk compared to an original Mark One and a high quality replica made back in the 60's.

Current trash.  Note the weird shape of the handle.  It's smaller than an original and very rough, porous brass.
The scabbard is two pieces of thin steel "sort of" crimped together and falls apart.  The clips are thin steel, spot welded and come off easily.


A high grade replica from many years ago.  The handle was made using an original as a mold master and is made of bronze, like the original.  The blade is stainless and the same thickness as the original, but not shaped the same as the original.  I've never been able to find out who made these or when.  Quality is as good as the original issue.  The scabbard was home made.  


An original Mark One.  The handle is actually bronze.


The only thing I could recommend is to try to find one of the older Japanese made replicas.  Where, I don't know, since they stopped making them in the early 80's.
If you just have to have something the crappy new ones will just have to do, unless there's something out there I don't know about that's better.

If you want the current replica, the price is $20.00 AT MOST.  Scalpers try to sell them for more.
You can buy them a number of places.  Do a Google search for "trench knife replicas.  Here's a couple:

http://kennesawcutlery.com/product/Daggers/Historic-Daggers/Replica-WW1-1918-Trench-Knife/pc/3235/c/0/sc/2343/156794.uts

http://www.brassknucklescompany.com/CRE/knuckle-knives

http://www.selfdefenseproducts.com/Historical-Replica-Knives-p-1-c-623.html

I would love to have one as well. Why is no one making quality replicas of these?

I do a theatre conversion using an ontario,case or any other Kbar or MK2 type with a pinned pommel.I get a $25 1917 trench knife copy as it has a stamped steel studded D guard 1/4 inch thick and I mate that to the MK2.While ive never seen a period made one or know if it ever was its not beyond the realm of possibility that it might have.Have seen original conversions of the MK2 blade mated to a brass cast 1918 knuckle grip.

perhaps one of our resident guys can come up with something?

I have an original my grandfather was given when he left for WW2. It is in great shape too.

Try looking at some gun shows I see them there quite frequently.