Balbinus on RPG.net responds to someone asking for sourcebooks about running a campaign about the whole concept of PSI powers:
“IMO the best is a game called 23rd Letter, it’s basically Firestarter (the Stephen King book/movie) the rpg. Probably OOP but available I would have thought on ebay.”
Thanks, Balbinus!
It’s not out of print! You can buy The 23rd Letter from Key20!