Flexible Urethane Foams
I came across this: http://www.smooth-on.com/foams.asp
I also contacted smooth-on for advice on what density foam I would need for a seat cushion and bolster (from inspection - the factory seat cushion was made from a pour-able foam cast in a mold).
In any case -- just passing this info along. Not sure if anyone will need or use this - but I keep a list of suppliers just in case someone I know is looking to do something ;) If anyone else knows of another supplier -- let me know. I probably won't go this route ($100+ for 1 seat cushion is a bit steep) but it may be an option :P