hey fuzzy,
as far as I know, there's not a marketed convertor....which sucks ass cause I've definately wanted to use one before (had a pimp arcade stick on DC, but none on PS1/2.)
Recently, I've come across a page that deals with hacks and kitbashing of console units, accessories, and video signals.
GamesX - Lots of useful info for that here.
Their sister site, AtariLabs, also has some useful info.
There isn't much on creating convertors for controllers, but since a lot of them are out there...i'm thinkin about starting a little page about it...i dunno. The GamesX page and AtariLabs page both point you in the right directions.
If you need help figurin it all out, I'd love to help...i've been meaning to mess with it all myself, just lacked the enrgy to start the project...haha..
-jin