Find a SAR team in your area, they usually have a recruiting page. SAR is not a casual volunteer commitment they tend to train a lot. The process here (alameda county ~ bay area) is take orientation class, apply, pass fitness/skills test/oral interview/background check, attend meetings and basic training, then train more while waiting for a call out. They want 6+hrs/mo to stay active. This will be different for every jurisdiction so ymmv.