well you can actualy get kicked off the board for naming other sites, even if they do have things that saltwater fish doesnt, because they want you to be faithful. Do a serch on google, or go to your local fish store and ask them to order you one, you will pay more doing this, but you will get to see what you buy.
And by the way, by hard things, i mean crunchie foods. as i said before, puffer's teeth grow constantly like a rodents because they eat mainly crustaceans. Also like a rabit, they need foods that will wear down their teeth like in the wild because if the get too big, they wont be able to fit any food in their mouth Some examples or crunchie foods are krill, crabs, or for any picky eaters, live feeder shrimp. And to make sure they are wornn down enough, you can place the food on a piece of live rock. The extra roughnes from the rock will file down his teeth
as far as tank mates go, that all depends on the size of your tank. If you have a large tank, your options are pretty high, but smaller tanks, they get low, since you are looking into getting a porcupine, im assuming you have a large tank, but how large is it? Any fish like triggers, large wrasses, larger angels, smaller eels, the types of agressive fish. If you do not want to go all out agressive because you may already have some fish in there, then that limits to the actualy puffer you get. I jsut got back form my LFS and i saw a porky that was about 4 inches long attack and kill, then procede to eat a goby about 3 inches. If you also keep him well fed this will reduce the risk. It would be best to stay away from the fish with realy realy big fins.
To exile; only some lions need big tanks. some dwarf species like a fu manchu only get 4 inches and will do well in a 30 gallon tank.
And by the way, ive only been in this hobby for 4 months, ive just been spending a few hours aday cruising theses sights and getting opinions, as well as reading them.