okay, so tanner is always riding with a bunch of people so you can't steal his, so is simon, my best bet is fly to wherever Jon is building a jump, If he is building but doesn't have his helmet on you may be able to grab it if you can run fast...
but they don't sell them so noone gets them other than pros, so you may actually want to just start throwing double cork 12s and 14s...that may be easier than stealing jon's...