PerAd,
Go through whichever AFCO you are working with - ask them to arrange for you to visit the Stations that operate the aircraft you are interested in. Most sqns are quite happy to host prospective aircrew. The AFCO should, if they are any good, be able to hook you up with someone relevant - Suggest that they go through the respective Force HQ to coordinate your trip.
Probably worth looking at all the options while you are at it - for example, you may have your heart set on being a Puma Crewman, but you may find yourself in the back of a Nimrod.... (or vice versa).
Good luck and all the best.