The Pete and Jakes tubular crossmember is terrific. I have one in my '34 project. I'm not sure they sell it separtely, but I'm guessing they do.

http://www.peteandjakes.com/20-27.html

Click on the catalog page to take a look.

Mine is a little different from that one since my body is channelled.

http://www.members.cox.net/otb_vigil...09_26/rear.jpg