No solid numbers for you, but I can say this......
All the "USMC SNIPER" Unertls I have seen were in the 1xxx series, meaning no more than 1000 of those could have been produced.
The "10X SNIPER", 2xxx series was reserved for law enforcement, and I understand only in the neighborhood of 83 of those were produced. (Just trivia for you- not USMC contract as per your question)
Likewise, there was a "C3 SNIPER" series made for Canada's Parker-Hale C3A1 , and the couple I have seen thus marked were in a separate 1xxx serial number series (separate from the "USMC SNIPER" 1xxx series). (Obviously, also not USMC contract)
Then there was the "USMC 50CAL.", 5xxx series made for the .50 cal. Barrett.
Only the 1xxx series and 5xxx series were USMC contract as far as I know, meaning that a maximum of 2000 Unertls could have been produced under USMC contract, if I'm thinking through this correctly.