I managed to get my hands on a real Remington M24 trigger (NSN: 1005015118314)!
This is the correct trigger for a M24, M40A3 or M40A5, and one of the parts needed for the upcoming M40A5 build. . Please see USMC M40A5 Build- Part 1: Gathering the Parts for more information on the project.
There aren’t many out there unless you want to pay a lot of money and I was fortunate enough to find one for a reasonable price.