First off, welcome to DTT. There is a lot of information already available on this site that you should be able to find using the search feature in the upper left hand corner of the screen. I also occasionally do a google search using the phrase "site:dotheton.com [search terms]", which produces better results when you're looking for something very specific.
As to your question, there are a number of tanks that have been fitted on CB350s, but it depends on your definition of "fit". Almost any other year CB350 tank will work on yours without any modification, as will most CL350 tanks. CL tanks are typically shorter than CB model tanks, though, so there may be a larger gap in between the tank and seat. For any other tank, you will likely need to modify the front and rear tank mounts on the frame and possibly enlarge the tunnel under the tank in order to get a solid fit. I have seen CB350s with tanks from larger Hondas, similar size Yamahas (RD350, etc), and even some old school chopper tanks, so anything is probably possible with a bit of work.
