You may not be able to find a vet who knows about feline diabetes. Let's face it, vets have multiple species and countless diseases, conditions, medications and treatments that they have to deal with. I don't expect my vets to know everything but I do expect them to care and to do their darndest to find out what they don't know.
So, if you can find a vet who is willing to admit they don't know, willing to spend a little time to learn, willing to think critically about new information, willing to consult experts, willing to do things differently instead of complacently saying "we always did it that way", willing to explain their logic and not dictate ... then that's a good vet, in my book.
good luck,
laur