No where is it written that a certain breeder has to sell you a dog, nor that you have to buy a dog from a certain breeder. Most breeders will require that pet pups be spayed or neutered. There does seem to be some resistance to this, especially having a male neutered. In my opinion, it is only common sense to do this. These are the two big killers of unaltered dogs.
Altered dogs can and are eligible for all performance events and ranch work.
The only two restrictions are that they cannot be shown in conformation classes and cannot be bred. Or you just may want a different line than the majority in your area. Or you may want to import a dog from another country. In these cases unless you can go and visit these breeders, you will have to buy sight unseen and have the pup shipped to you. Complete communication and confidence is a must.