It's pretty simple to purchase rifles (and other things like parts, accessories and surplus ammo) through the CMP. You can get the order forms off the CMP website here:
http://thecmp.org/cmp_sales/rifle_sales/ordering-information/
You just have to print and fill out the order forms, get the eligibility form notarized and submit the forms along with proof of age, citizenship, membership in a CMP affiliated club and proof of a marksmanship activity. The eligibility requirements and proofs accepted (or forms for such) can be found here:
http://thecmp.org/cmp_sales/rifle_sales/eligibility-requirements/
As for the CMP affiliated club requirement, I'd suggest joining the Garand Collectors Association:
http://thegca.org/
The GCA is simple to join online only costs $25 per year, and you get a quarterly magazine for your dues. Plus, the GCA sends its membership list to the CMP, so they can just look you up after you join.
As for the 1911's, the word is that even the worst condition junkers will be $1000+.