I have several Steam keys and Gamersgate Mac games that I'm willing to give in exchange. I don't know if anyone will think this is a good trade, but I figured I'd put it out there.

Steam:
Ironclads collection (Ironclads 1-5)
Bad Rats
The Ship Collection (steam gift)

Gamersgate:
Cities in Motion (Mac)
Dark Scavenger (Mac)
Fortix 2 (Mac)
3079 (Windows)

Can't help you, but you could also try in this thread, since most trading is done there:

http://www.gog.com/en/forum/general/classifieds

Good luck :-)