Are there any Mlok or KeyMod rails that use a standard barrel nut?  I don't want to have to remove my barrel nut if possible so looking for options that might be out there.

The Fortis REV II uses the standard GI barrel nut. It is an excellent rail. Fortis makes high quality parts.

Fortis is probably your best bet

https://www.aimsurplus.com/product.aspx?groupid=2680&name=Fortis+Rev+II+Free+Float+Rail+System

Troy makes one I believe as well as Centurion

Removing a barrel nut is extremely easy though and opens up a lot more options. A Geissele rail install is as easy as it gets

Samson

The Fortis REV II looks pretty nice.  Looked at Samson but didn't see one that used the standard barrel nut.

Sorry, I should have been clearer.  Samson offers their Evo series hanguard in a KeyMod variant.  This uses a standard Mil-Spec barrel nut.  What may have thrown you off is that they provide a two piece thermal bushing that wraps around the barrel nut as part of the mounting interface as well as being a thermal insulator.  I mentioned this rail because I own one on my 9mm SBR build where I have the rail partially enclosing my TiRANT 9 suppressor, so I know it uses a standard Mil-Spec barrel nut.  Here is the (corny) video that convinced me it was a good solution for me as it could use attachments even at the suppressor overlap:

^ Thanks for the info.  I have a Centurian C4 that came on my BCM upper and it's nice but it a little heavy.  Might give the Fortis Rev 2 a try and see how I like it.

I was once in your boat OP.  Buy a reaction rod and it simplifies so many aspects of upper building.

This is what you need:
Troy SOCC M-Lok rail

Basically all of Troy's rails use the standard barrel nut, just shop around their site to find what you want. Primary Arms has had good deals on their rails lately.

Friends don't let friends support Troy

FWIW, I have 2 Fortis Rev II's in in the 9 inch M-lok flavor, and they are great rails. Machining was top notch, install was easy, super light weight, and so far they seem pretty damn durable for a 2 piece rail. Really nice and tight lock up on the standard barrel nut. Only catch is on a FSB barrel you will have to remove it to get the rail on there, but its really not hard, just an extra step. Moving forward, for a rail that uses standard barrel nuts, Fortis may be the only one I buy moving forward. I've used DD Omega rails and Centurion's rails and they are great, but they add a lot of unneeded weight.

Troy M-lok rails have the "advantage" of having M-lok slots on 7 sides, while the Fortis Rev II only has slots at the 3, 6 & 9 o'clock positions. The Fortis rails have a better attachment method for the standard barrel nut. They are also lighter than the Troy rails and have built-in QD sockets if you use QD slings. I have both and like both, but I've been going more towards the Rev II lately when I can find them on sale.

The Fortis is a nice piece. My wife has a original rail and my step son has a Rev 2. Both are light weight and perform as advertised.

The company is top notch. After getting the rail installed on my wifes rifle I could not tip the upper open far and contacted them. They asked for pics and while taking the pics I noticed the front lugs on the lower were larger then normal, it was a light weight lower and the manufacture beefed up the lugs which i did not see before. I sent the pics and notified Fortis that the issue was not with there rail and was with the lower. The piece that is removed and covers the bottom of the rail around the barrel nut needed to be modified to fit the lower. I advised Fortis of this and asked how much for me to buy just the one piece as I wanted one on hand in case I screwed it up modifying it. They asked for my address and told me not to worry about payment. I got the part a few days later, they are a very classy act. My next build, not sure what yet, will have a Fortis rail on it.

Nothing wrong with my Troy rail.  I wouldn't hesitate to buy one of theirs again.

On the cheaper side, Midwest Industries sells a couple 2 piece free float rails in M-Lok that uses the standard barrel nut, also quite a few different RIS handguards.