Sounds to me like you have a bunch of greedy vets in your area. I can't think of a clinic in my area that WON'T do a chicken fecal. And two will see chickens, but that doesn't make them specialists.
It doesn't matter if a vet sees chickens or not. They ALL can do a fecal float on chicken feces. The parasite eggs are the same no matter which animal excreted them. I would take a combined sample in to your regular vet.
A poop picture will help. They could just be shedding intestinal lining...