The BladeForums Exchange is probably the most popular, but there are lots of gun/knife forums you could use. Additionally, there's a yahoo user's group:
bussekinexchange · Busse / Swamp Rat / Scrap Yard Exchange (See the "Where can I get old models of knives" section in ColdOne's READ THIS! Rules & SY Info sticky thread).

Finally, I noticed this link:
Busse Kin Exchange in Andy Wayne's signature line page of links.