If you have time, give this a try.. call up vending machine dealers and ask it they have any CO2 tanks for sale or they want to get rid of. I scored 3x 15lb tanks (2 were free, and 1 was $20). Tanks that size are primary used for soda fountain applications and are usually pretty old. The oldest steel one i've had was made in 1937 (pre-WWII!). It doesn't matter how old b/c most places do a tank swap and regularly check tanks every 4-5 years.