I got my first collar at 13^^
I just asked if I could get a collar for the dogs and then got a third one I liked, bought that and said it was if the dogs collars didn't suit them.
So maybe you could ask for money then a little later ask if you can buy a new collar for the dog/s(This'll only work if you have the same size neck as your dogs,so maybe say it's for your friends dog?)
Or you can just ask for some money(around the same amount as the collar) then sneak to the pets store saying you're looking at the dogs(If the store sells animals, if not say you're looking for a dog bed for yoour pet or something......) then pick out your collar and buy it then put it in your back pack^^ The they'll never know >
I wouldn't recommend the super sneaky option because you might get caught!