Halflight,
Try National Balsa in Ware, MA (New England). They have triangular stock in balsa/bass/and spruce. Quick service and good prices.
Note that if you plan to attend the Toledo RC Expo on April 6-8th, Nat'l Balsa is an exhibitor and usually has a HUGE stock of balsa and other model wood products for sale at show prices and no shipping.
Regards,
Art ARRO