I think that being a member of the
Garand Collectors Association (dues $25.00 a year) would qualify you for purchasing a Garand along with firing in a CMP match. My club offers a couple of CMP matches a year and individuals that are not members of the club are welcome to shoot. Charge is $8.00 and the club provides the ammunition. Many clubs do this.
I just checked on this and being a member of the
GCA qualifies you and, if I read it correctly, prior military service exempts you from the 50 round CMP match.
Go to:
http://www.odcmp.com/Forms/1orderform.pdf This has the complete requirements for purchasing a rifle and a phone number for CMP. In order to purchase parts and ammunition you have to belong to a club that is affiliated with CMP but not for a rifle purchase.
I think you will be able to make a purchase through CMP with no problems.