I have not found any of the commercial MV stencil makers to produce accurate 'modern' USMC sets (by 'modern' I mean markings for roughly the last 30 years).
However a local print shop can probably produce what you need.
I don't know if you have original markings on your vehicle to reproduce, but the following is generally what you need.
Note that Marine markings follow a standard pattern, but can wander a bit in application.
And they change over time - modern markings are slightly different from Vietnam-era markings, which differ from WWII era.
The lettering for the vehicle ID (USMC and the 6 numbers) are done in MD Military A font. The characters are 2" tall, with 1/4" stroke. If you'll notice the M, it looks like a V with legs. On Humvees, this is usually on top of the hood on both side, and centered on the tailgate.
The one exception to this is Oshkosh, on vehicles that come lettered from their factory they use the font used for most other military stencils, which I believe is Gothic BE. Oshkosh lettered the vehicles their way, regardless of standard USMC practice.
The individual vehicle serial number is always 6 numerals, no letters. The first two numbers indicate the series, most Humvees are 61xxxx or 62xxxx. (The latest production ones may differ slightly, I haven't checked lately).
The only normal unit markings will be an RUC, in the form of an M followed by 5 digits. An example would be M11160 (1/5 or 1st Battalion, 5th Marines).
This will be applied in 2" characters on both sides of the vehicle, usually on the doors, "somewhere" on the back, and often on the front. Since Humvees originally had removable doors, their RUC number was placed on the side below the door opening, this low placement followed into hard-door versions.
Most of the rest of the stencils on Humvees are done in 1" characters. USMC vehicles tire pressure used to be applied as the number followed by PSI, but the Army version of TP followed by the numbers has been creeping in over the years and is now as common as the PSI version.
If you want to go that far, there is usually an embarkation code on most vehicles, on or near the front right. On Humvees, it is usually on top of the front right corner of the hood.
If you need them, I have a bunch of photographs taken in motor pools on Camp Pendleton, and the museum out there, that I can share.
Cheers