Do you need excactly 7/32, or will 5mm do the job? I find many of my small diameter tubing on ebay.
If 5mm x 3.4mm will do, try this
http://lmgtfy.com/?q=blade+400+main+shaftfor the RC-helicopter mainshaft I am using. Beware that some are solid, while you probably want the tubes. Might look in your local hobbby-shop as well?
Brgds,
Ed