You only need to get them popped/probed once, generally speaking.
If you buy from a breeder, they can pop/probe it for you on the spot.
If you're lucky to have a local reptile store, someone there should be able to do it for you free of charge.
Some communities have local herp groups on facebook and what not, try and find someone willing to do it for you.
If you take your snakes to the vet on a regular basis, the vet will be more than happy to do it for you as well (duh).