I've heard of a guy down-grading an E-Mag into a mechanical marker because he just liked the look of the front grip. I'm not sure if the front grip/battery pack is part of the body, or if it connects just like a front grip- but if it does, you should be able to buy a replacement battery pack (some people sell them) that you can mount to your mini-mag.
It seems like it'd be a bit huge looking on a mini, but it'd look hella sweet if it matches your mainbody. Is the mainbody you're looking at black, gray, or polished steel?
Also, I've seen people put regular grips on E-Mags (usually, putting their battery in the trigger-frame). So I'd imagine you can mount it like a normal grip.
So, ASSUMING IT CAN BE DONE, you'd still need to modify the battery pack to allow an air-hose through it, if you want it to be a gas-through. Otherwise, you could just use a hose straight from the valve to the ASA. If you can do that, then I'd suggest looking around either the Buy/Sell/Trade forums here, or head on over to automags.org and ask around at their forums to see if anyone has one for sale (you'd be surprised the things they have there!)
Naturally, and out of good faith, I'd reccomend you try here first, though.
