Disney ringtones are VERY hard to find nowadays....there were LOTS of them for a while (most of them bootlegs) and then most of them disappeared about a year or so ago. They're still available in Europe, but unfortunately those ringtones don't work in the States (I'm assuming you're in the States).
I would start at the homepage for your calling plan. AT&T has a Disney ringtones you can pay for. Verizon has none (which is why we're dropping Verizon when our contract expires). I would also suggest doing a Google search for "ringtones U.S." and see what you can find.
Good luck! Wish I could be more helpful.
-Sharon-