archie,
as I said above you ought to check out the two local area clubs...
WAMAS (of which I'm a member...) is have a social this saturday... check out the website for more details...
We usually have meetings ~1/month... (some official like the social, some unofficial like food making, or building parties) at those meetings there is always frag trading/selling, and most likely there is a thread about what is going to be traded at our website.
Now that being said, we do charge a $20/year fee for members. That gets you in free to all the meetings (inlcuding a great list of speakers, frag trades, water testing, and discounts at many local stores)... well worth the $20 if you ask me.
I'm not trying to discourage you, just there are allready existing networks doing just what you say in this area.
Dave