"Industry Brand" and "Air Gun Inc" are definitely not mainstream and you're probably only going to get a "Tell me where to go" response out of this. Certainly from me you will!
My guess is that both of those brands are either Chinese copies of a different rifle/pistol or they are re-branded guns originally made by one of the European manufacturers. Diana was quite prolific at this after WWII when certain restrictions prevented them from making air rifles in Germany. All of their work got farmed out to Scotland where their guns were re-branded for other companies. Or something like that, the details are somewhat fuzzy to me.
In any case, I haven't the foggiest what sort of guns you have or where to get parts. I'd suggest going to the
Yellow Forum and asking them. Lots of traffic there, I'm sure someone will have an idea.
Clark