You could try to necro them like you did this thread... ba-zing!
But seriously... probably buying new ones is easier than trying to resurrect yours (I'm assuming that your KJW mags are leaking, correct? Or do you not have a propane adaptor yet). New ones from overseas at $20 USD a piece, plus shipping. Brand new from most retailers, they can be found at $40 a piece in Canada. The choice is yours... there are just too many possibilities for potential dried up/cracked rubber bits to warrant trying to fix them, IMO.