I know he is a purebred because I have studied the breed and met his parents when I got him but they weren't registered (I don't think). He came from a farm for $100 but my dog would beat the other Australian Shepherds, I just know it!

Just because you have met the parents does not mean the dog is a purebred. Chances are that you would have paid a lot more than $100 if it was pure bred. Some breeders sell puppies cheaper, but only if they are not show quality, so it could be that even though you think your dog is tops it may not be. To enter a dog in a show (even agility) it needs to meet the breed standards, and be registered. You will need to provide papers proving that your dogs, it's parents and grandparents were all registered as purebreds. Even smaller shows are strict on this. You can't call your dog purebred without this document.There are sometimes open events, in which any dog can enter, but are few and far between.If you really want to show your dog, go back to the farm and get the papers. You wont get far without them.