Well, on the sohc you can technically use any tank from 69-78, they all fit. But for your purpose, anything from 69-76 would fit best.
As for new tanks, you might be able to find a NOS tank(new old stock, if you didn't know) but it will be a pretty penny.
Most people just get their current tank fixed if possible. There are new tanks you can get but not stock, and they will run $400+ generally.
The ride IS the adventure. The destination is just to get gas!