The best place to get the tank is locally, at a welding/medical supply store. As for the rest, look at Ebay. I'll get you some links here of what I have on mine....
Regulator - http://cgi.ebay.com/Ma957-CO2-REGULA...em330086958420
Limewood Airstone - http://www.bigalsonline.com/BigAlsUS...bywoodairstone
Powerhead - http://www.bigalsonline.com/BigAlsUS...owerhead160gph
What you do is follow the instructions closely when installing the regulator on the tank. If you don't, and one of the valves is even the slightest bit open when you open the main valve on the tank, you will blow out the guages. If you get the regulator and need help, I can help you get it set up at that time.
Also, when putting the regulator on the bottle, it needs to be really tight. Use the proper wrench for putting it on. Also, if you have a bottle of Windex, you can spray it around the connections, and if it's not tight enough and is leaking, it will bubble.
Once the regulator is on and the valves are closed on the regulator, open the main valve on the tank. Then check for bubbles by spraying with Windex on the connection. If no leaks, then go ahead and fill the bubble counter with distilled water, put the cap back on, install the CO2 lines and airstone and powerhead. Then you are ready to turn the CO2 on.
On the milwaukee regulator, the first step is slowly turn the big black knob on the front (opening the valve) til the secondary pressure guage reads 8-12psi. Once there, slowly open the needle valve til you get about 1-1.5 bubbles per second. Then you are set. Monitor your CO2 levels in the tank, and if it's not enough, turn the bubble rate up a touch. If too much, turn down a touch. Withing a couple days, it will be set and you won't need to mess with it much til it's time to refill.