Acey from NESWorld has a picture of a PC -> FDS cable in his FDS review (http://nesworld.parodius.com/famidisk.htm), but unfortunately he doesn't have any additional information about it.
But btw... were you ever able to play that pirated SMB2j ROM on your Doctor PC jr? That's one of the only FDS games I'm *dying* to play on the real thing :)
-- Matthias
P.S.
Bleh, I should be more careful when using html tags in my posts... >:/