i've been thinking about getting a show dog, but I have heard that you can ILP purebred rescue dogs and show them in Jouniors and at specialty shows 9I read in an AKC book that said that), but...

You can sometimes find quality dogs (papers included) in purebred rescues. Keep in mind, that many shelters & rescues alter their dogs, before adopting them out, which disqualifies them from the main dog shows (dogs have to be intact).