Gates of Hell can be found at good ol' DiceFreaks. We might also be willing to salvage some stuff from A Light From on High if the old bloods will let us. Tome of Fiends is by Green Ronin; you can still get it PDF just about anywhere and print from LuLu. I -highly- recommend getting it, even if you have no investment in this project. It's on of the best, most vile, detailed, and flavorfully written monster books in all of d20, easily outweighing Fiend Folio.

Now before I agree to anything, what's this 'minor power' stuff here?