The MC012 and MK012 designations are variations in the rendering of the Cyrillic alphabet, whether you spell it microphone or mikrofon. This has to do with who the importer was, and whether the mic was originally intended for export. They are the same mic. GC does indeed sell Oktava mics, but only semi-officially. Not all branches carry them, and they have mostly given up advertising them. I have bought them for $60 apiece at the Natick, Mass GC as recently as a month ago. They will usually charge $99, but I have a fair amount of buying power at GC.
The Sound Room is a whole different animal. They do excellent quality control and meticulous matching, and charge you a fair amount of money for it. Taylor Johnson at The Sound Room is knowledgable and helpful. In either case, I would not buy them on ebay. If you want them cheap, find a GC that has some, and plug them in before you buy them. If you are not a gambling man or an audio expert, consider paying the Sound Room full price for mics you know will be in good condition. I've done both, and gotten good mics both ways.-Richie