The C220 uses only 12AX7's, 2 for the line stage, and 2 for the phono stage. The C2200 uses 12AX7 and 12AT7. I think Matt's recommendation for Mullard is good, although there is many different ones, depending on vintage and some made for military. Have a few friends that like Telefunken, also some variety, in their MAC gear. Here is a link with lots of information on 12AX7's from another reputable dealer.
http://www.audiotubes.com/12ax7.htm