We have a local supplier of biodiesel fuel and I am thinking of
converting my '95 Geo Tracker to run on it. Am looking for conversion
kits that my local friendly mechanic could work with, or
people/companies who do conversions, preferably located in the Pacific
Northwest.  Another possibility is to buy a new or used (cheap,
anyway) car that is already made to run on biodiesel.

possibly you could get a new biodiesal engine and use install it in
the old car. that seems to be the only way.

Deisel engines easily accept biodeisel.  You need a deisel vehicle. 
There are deisel trucks, some VW passenger cars, and some Mercedes.

Go to website WWW.greasecar.com they will have what you need. This
sounds very doable. Good lick let me know how it works out for you.