NessMcCool you're in Montreal, go to LL Lozeau (upstairs) they usually have some.
One of the quickest ways to spot if duster is 134a is to check the can warnings for flammability: di- (HFC-152a) and trifluoroethane (HFC-143a) are flammable, tetrafluoroethane (HFC-134a) is not. Which is why camera places carry it (you don't want to spray something flammable into a bunch of high-voltage capacitors).
It's the same product Rugger_can pointed out.
Edit: I have to ask, WTF are you shooting that runs on duster anyway?