There seem to be three elements of a cafe racer. One is the tank. The seat . And then a certain space under the seat. A see through quality that is sometimes difficult to achieve.
For the tank there are three quick choices then millions of others. 1 stock tank maybe fill in the fairing attachments. 2 a tank from another motorcycle. Need to modifie the tank or the frame to work. 3 full fabrication . There are plenty of places that do the work. Expect to pay for what you get. 1000 dollars for a good aluminum tank that does not leak is a good deal.
Air tech sells lots of body parts. Again you get what you pay for.
http://www.airtech-streamlining.com/
This is my 2008 cafe racer.