Hmm, I'm trying too think of some low-key way to start up in a very small way to explore the interest.
People interested in offering some of their seeds this way could make categories within their plant lists.
Then send links to their categories.
I would post those links a blog article or whatever else Dave suggested, and I would update as more people joined or dropped out.
The key element would be Dave posting a prominent link to that page-of-links.
BUT maybe we want to wait until someone thinks of a very low-overhead way to keep it from attracting seedy-greedy people. Jonna suggested limiting it to no more than 5 (or 10) requests to each donor. Maybe that is enough deterrent by itself - the limited number of requests plus $2.50 to mail a bubble mailer will cost the requester 25-50 cents per pkt.
Or, if we do tie the seeds to the existing acorn system, that would certainly motivate new members to contribute photos, data suggestions or whatever!
I strongly assume that people who already have hundreds or thousands of acorns from database contributions won't be rushing to acquire dozens of packets - they probably have specific desires for specific varieties.