walkerita, I believe that it is very important that the instructor (s) are great realistic painters themselves. If they are not, they won’t be able to teach you how to become one yourself, as they won’t have the necessary skills.
Grand Central Academy of Art in NYC and Jacob Collins are great. The best known ateliers (school for realistic art) are the Florence Academy and Angel Academy of Art, both in Florence, Italy. My daughter studied at both. She is a full-time successful professional realistic painter. She highly recommends the Florence Academy of Art, but knows Jacob Collins well–she sought him out for advice about 12 years ago.
A list of good realistic painting schools can be found on this website. Some of them are colleges, but most are not. Grand Central is on this list as well: