I just picked-up a brand-new 28.6mm Campagnolo Record, from the late 1970's, on eBay for $10. I found this as I have a good old-fashioned vintage bicycle that requires the 28.6mm. They are getting scarce. But I also recently bought a Shimano FD - and it came with clamps for all the sizes.

In that Shimano (not always) sends these along with the purchase, your LBS may have a bucket-full of these clamps. Make a few phone calls.