You need a higher quality air and a higher pressure than what is provided with traditional compressors. Basically, for and HPA tank, you need the kind of air that would be used to fill scuba tanks. If you have a compressor that can do this or a spare tank that you can fill, you can buy an adapter to fill from either of those.
Not specifically this, as there are others, but you'll need something like
THIS
Also, you can't use your CO2 tanks to fill this air. You need a
HPA tank. Trust me when I say that it is better to not go cheap on a tank. Get a carbon fiber one that is at least a 68/4500. CF is more lightweight and a 3000 size tank can easily be blown through in a short period of time.
If you have more specific questions, there are several good community sites. Check out:
http://www.98og.net/
http://www.a5og.net/
http://www.x7og.net/