To clarify I’m interested in treating both peds and adult patients and not limiting my inquiry to the pediatric specific pain fellowships.
My fault. That's a very different question. At that point they're just looking at you as a neurology resident. The usual pathway is fine, but you'll want to establish relationships with PDs at the place you're looking at. Your application may be stacked as compared with a conventional anesthesia/PMR person as you've had a few more years to pad it with things, but you need to establish that you have had exposure to pain (good letter from your local program) and that you're trainable.
1. Look at places with large classes, ideally 4+, as you're going to find them more willing to take atypical people due to the risk of a bad fit. The fellowship is just a year so it's a lot easier to take people that're already knowledgeable about things and polish, rather than really train them up.
2. Reach out to those PDs when you've got things figured out. A good time may be the gap after the rank lists go in and before the match happens for the year prior. In this case the first two weeks of October might be a good time.
3. Get to the interview stage and figure out how they train non-Anes/non-PMR people. Show insight into your weakness/gaps, and then give them comfort by talking about your exposure to stuff like clinic flow, procedures, reading MRIs, etc.
It's a sales thing. Good luck.