Are you currently a resident, or a med student getting ready to apply for residencies? If you are in the med student/future resident category, I would suggest looking at residencies that have a good allergy/immunology "presence" (and maybe even a fellowship). Even if you don't want to stay at that program, the networking that might be available could be helpful. Plus you may get more exposure to that specialty to help confirm your interest, and you may also have the opportunity to do a little research during your residency.