I found Centerfire Systems to have all Cetme, G3 parts and a ton of them. Mags for 2.99, Stock sets for under $30.00, springs, fireing pins, buffers,oh my. Outstanding selection.
There's also a seller on Gunbroker, user name is Van Loos. I've bought from him before. He's in Spain, so he has access to a lot of CETME, Astra and Star parts that don't show up locally often.
For obvious reasons, his shipping times are not quick. Always got good parts from him, though.