Can you not just cut a bit out of a full circle one?
It took us a long time to get the doctors to use the bite guard at one place I worked but the managers soon stepped in when they kept on getting £40k bills for new TOE probes.
I once saw what looked like teeth marks on a scope for looking up the other end. Had they just used the wrong scope as the correct one was not to hand or just pushed it too far in?

Robert