(I browse ioffer)
and there doesn't seem to be any fakes m51 jackets out there.. yet.
and yes, there are fakes of the mechanics. In fact, the most common fakes I have seen are the ugly leopard nuptse jackets which I think are slowly creeping onto ebay, the TNF mountain shell, mechanics jacket, and the leather down jacket. But hopefully if you're willing to drop that amount of money for those pieces, you're going to do some research before you pull the trigger. but I really only know of ioffer.com as a source so there may be other fakes sold elsewhere I don't know about.
keep the questions coming. I'm happy to help.