you can use any radioactive stuff in a dirty bomb, it's just that there is a lot of spent uranium out there. But you're right, you would need a lot of the stuff they sell, but when you have billions in oil money.....

that place also sells metals and chemicals like thermite and a thermite activator. Crazy.

Sodium metal is pretty cool though. You can chuck that stuff into a pond and it explodes and pops and jumps around.