Can you use an air compressor to fill the ballast tank in a caswell gas system with air instead of propellent from can ?

No, because it need change of gas state into liquid to have that much volume inside a tiny space. To compress such a volume from gas to gas might burst any tank designed just for that propellent.

I company Alexander Engle from Germany uses stainless steel motorized pistons. They are perfact and don't need to be recharged,