Sorry.. Forgot to include the link from another's post:
http://www.onlinemetals.com/merchant.cfm?id=904&step=2&top_cat=79Nickel silver used to be sold by K&S and was great for making tanks..
Actually, making a fuel tank isn't that bad, quite fun actually.. You just have to anneal the brass or copper tube. Lee's Machine shop sells a very handy tool for making the bends straight.
1 fl oz = 1.804 in^3.
The advantage of making your own tank is you can get it exactly like you want it.
I haven't tried Sullivan or DuBro clunk tanks, although I probably will eventually.
Sorry for the confusion..