Mg and thymoma kind of go hand in hand. I don't remember the exact numbers, but I think it is somewhere around 75% of thymoma diagnosed patients have, or will get MG. MG is usually what leads to finding the thymoma tumor.
Sounds like you are early in the process of diagnosis yet if the MG lead to the thymoma diagnosis. That may be a good thing sing patients that have MG which lead to finding a tumor usually are in earlier stages which are very treatable
I do recommend that you seek treatment at a larger clinic. Most local oncologists are clueless regarding thymoma. If you are in the midwest I would strongly recommend University of Indiana at Indianapolis however, others like MD Anderson, Mayo Clinic, Stanford, Sloan Kettering, etc. would also be good.
Dr. Loehrer at IU is recognized as the formost expert on thymoma in the US, but most of the rest of the big regionals mentioned will consult with him for Thymoma cases and know of his work.