You can still order a new mag from AGD, and there are plenty of mags that run on HPA. I think AGD was the first to introduced HPA. I would suggest an automag with an RT valve. Quite a bit of information can be found at
and you should be able to pickup a good one in the forum here. If you want an inexpensive automag classic, pm me.
A rugged woodsball option would be the Tippman A5. The new GOG Enemy is a good cheap new option too. If you want retro, check out mcarterbrown.