http://www.seedliving.ca/ this is the home page -- buy, sell or swap, globally, apparently!
http://www.seedliving.ca/sl/displayNews-55/ this is their new online swap option!
SeedLiving is introducing a new option so that growers can swap seeds in their community online, as often as they wish. Pass SeedLiving's URL on and begin swapping. There is now no need to list a price for a packet of seeds, you can only swap if you'd like. Simply choose the 'swap only' function when listing seeds. (read more at the link)