Thank you, @erikas for your prompt reply. Yes, I have tried. My primary care physician said simply he didn't know, didn't know whom I should consult, and I was on my own. I have called local immunologists, allergists, and rheumatologists, all saying it wasn't their bailiwick. A call to Duke University Health System was a catch-22 (the support level personnel for their Duke Patient Support/Referral System was not knowledgeable enough to advise which specialty I needed to consult, and I was not allowed just to call one without a referral from my primary care physician, who had told me to find out which specialty first). I called the Infectious Disease Section Head at East Carolina University who was very gracious and informative about the new covid19 vaccines (saying he knew I should stay away from AstraZeneca at least as it would probably be lethal) and that mRNA vaccines were safer, but he really had no knowledge about Myasthenia Gravis or thymectomized patients. A very caring nurse at one of the endocrinologists' offices I called, suggested "try the Mayo Clinic. They know everything!" Here I am.
(I should add my original neurologist, with whom I stayed in contact for years, has long been deceased.)