airbrushing with tank

You can use CO2 or Nitrogen, the size will depend on how much money do you want to spend. They come in the range of several hundred pounds. You'll need a pressure regulator specially designed for this application, and expensive also, it should be available from the gas supplier.
The initial investement might be significant but it'll last for months (maybe years) till you need a refill.
The fittings for your airbrush will depend on what you already have but my guess is that you'll need a fitting from 1/2" to 1/4" NPT. Take your airbrush fitting with you to the store to get everything without mistakes. Good luck

Mario:
Thank you very much for your advice, it was very helpful.
Manolo

check this out.... http://www.finescale.com/fsm/community/forum/topic.asp?TOPIC_ID=1906

this is what i use

You do not want to use oxygen. It will suport combustion and could be very dangerous. Especially if mixed with fumes from painting. Use nitrogen or compressed air.

CO2 can also be bad in enclosed places because it will displace the O2 you need to breath, as will Nitrogen, Argon, etc., as stated above Oxycen is an oxidizer and be explosive. Compresses AIR would be the best.

May i ask, who suggested oxygen????