Search Amazon or eBay for "Spring Hose Clamps" and you should find what you are looking for. They won't be OE GM clamps, but unless you're doing a concours restoration, I don't think anyone would notice or even care. I got an assortment of 6mm-22mm for under $15 on Amazon.

Other option would be a pull your own parts place. Those would be OE if they haven't already been replaced with worm screw clamps. They should be very cheap there, if they even charged you at all.