for 1" threaded 20" suspension forks, try looking up places that sell stuff for folding bikes, and for BMX racing/dirt jumping. They exist! They are popular on recumbent bikes (esp the ones with the 20" wheel under the rider's knees)

http://www.bentrideronline.com/messa...hp/t-1833.html

http://www.google.com/search?ie=UTF-...uspension+fork