I think the problem was how you phrased your question, i.e. "how many different means of driving a dart down the barrel have members encountered?"

The literal answer would be: compressed air from bellows, compressed air from spring piston, or air pre-compressed in a reservoir. So there is not really much else to say.

Did you intend to ask about different types of cocking mechanism in the case of spring piston, or different types of reservoir in pneumatic gallery guns? If so, then I think you might then have opened up an interesting discussion.