@jozer Endocrinologists who specialize in bone health are hard to find, but they do exist. I know of 3 of them and all 3 are associated with universities. My guess is that there are more. I am currently on a path with one where the university clinic takes 10 to 12 weeks to evaluate a referral before they decide IF they will allow you to make an appointment 6+ months out from then.

There are other types of doctors who specialize in OP. If I have to start looking further, I would ask the expert who declined my case to suggest someone else, I would try to see if I could see who attended OP conventions such as the Interdisciplinary Symposium on Osteoporosis. There is a limited search tool for OP oriented medical people here, but I know that it does not include many, although Lisa Moore of Brick House Bones did come up:
https://www.bonehealthandosteoporosis.org/find-a-professional/
My doctor agrees with jozer that a random endo, not selected in advance for osteoporosis, is a long shot for significant OP expertise, far likely to know lots more about diabetes than OP.

For a specific example, here is an interview by OsteoBoston with Dr. Benjamin Leder who is an endocrinologist, researcher, and clinical practitioner in the Boston area. He mentions near the end that his office accepts appointments, but they are booked many months out.