Only a few supplements were published, and then the game was pretty much abandoned by 1986.
FGU, however, is still around, and all of the original Psi World games and supplements are available as PDFs at their site or on DriveThruRPG.
I’m thinking of running a one-shot of this, but I didn’t much care for the design of the original character sheet. It’s sort of ugly in a boring way, like a lot of 1980’s character sheets were. I’ve made my own 2-page fillable PDF version.
More of my never-ending parade of character sheets can be found here.