You can get the duster adapter from Airsoft Innovations, a Canadian company. That way you can just use regular duster cans. And no, HFC 134a will not harm a "propane" mag. The mag can handle either gas. Get the Airsoft Innovations gas gun kit, gives you the propane tank adapter, the duster gas adapter, and some silicon oil for lubrication.
The duster gas might have some issues cycling the slide, but read reviews and see if anyone said anything to be sure if it will or not. I've never used one, let alone with duster, so I can't say. But if it has a metal slide, it might struggle. The lighter the slide the easier it will be for the duster to cycle it.
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