I picked up a CO2 POWER TANK system and it was way more pricey than Bart's contact. I probably payed a lot more for the name... I was in a rush, so I didn't shop around too much.

http://www.powertank.com/products/sfID1/13/productID/26


I loved it, it worked really well. It's a 10lb tank that aired up 20 tires from 15 psi to 40 psi. I would get more tires if I only filled to 30 psi and then topped it off at a gas station.

As for compressed air in a SCUBA tank - I think that is more likely to be a bomb at the pressures you need (about 2 to 3 times higher than CO2)

I filled my bottle at a fire extinguisher recharger in Colorado ($20) who laughed at me a bit when I told him how much it cost me (~$600 with all options) - he said he could assemble one for ~$100 - tho not as pretty. The fancy regulator is where the money is.

FYI,
I also priced out an Oasis compressor 100% duty cycle as an alternate on board air system - $1200!!! for the 12V compressor. Now that's pricey!