A - get to know whoever manages the darkroom and offer to help out in the darkroom
B - get to know whoever really manages the darkroom (i.e. is actually there when it's being used) and offer to help out in the darkroom
C - get to know whoever really manages the darkroom (i.e. is actually there when it's being used) and ask for their help; sooner or later you'll have enough of a relationship that they invite you in (perhaps when no one is looking).