If you are looking for small metal tanks used for suction feed, they come up regularly on eBay.
If, however, you want something that is simple, effective, and best of all WORKS EVERY TIME!!! Then dump the suction feed and go to some sort of bladder type system.
It greatly simplifies everything. A great into to bladder tanks is on Hank Nystrom’s website: http://www.texastimers.com.
Bob Beecroft also has a good writeup on his site: http://www.theaerosmith.com.
There are a few holdouts on this Forum that still use metal, but most of those run diesels.
My life changed for the better when I switched to bladders. If you are using a COX engine with a starter spring, you don’t even need an electric starter. 🙂