Coming in late to the game here, but I shoot my service grade regularly and I'm glad I went with it over a show piece. My son has one that looks clean and neat (like your AR, Grendel) and it's a safe queen. As painter said, there's lots of ammo out on the market that meets Garand requirements so you shouldn't have a problem. I shoot mil-surp ammo I stocked up on from CMP (lake City stuff made in 1966 and stored in 20 round boxes in airtight ammo cans). And some Korean ammo in 8 round clips, several bandoliers to a can.
I can recommend the Service Grade. CMP wont sell it as a shooter if it isn't. Ugly dogs still bite.