AFAIK, I don't think you're allowed to post compressed gasses. would be good though
EDIT: Just found THIS but cant make heads or tails of it at this hour. :\
I know it seems like a big thing to buy for your computer, but if you're regularly going to use compressed air on your PC then maybe you should look at buying an air compressor.
Not sure of the price of them, but surely you could get one for fairly cheap that in the long run would save you money?