Well, I don't know if they ship, but here: http://hendersonvillehobbyhouse.com/
I haven't been to many hobby shops, but a very big hobby seems to be r/c planes. The two I've been in have had racks of 3' lengths of various profiles balsa for struts and spars and stuff. I just took a Sav filter with me. I'll bet any on line hobby store has them. Betcha Scamazon has them, too.