Mephisto Atlanta ROM is inside the Hitachi SH MCU. It's not yet known how to dump it.

Most remaining unemulated chesscomputers are either on MCUs with no known dumping method, or they are rare/expensive. In the latter case, when collectors let Berger/Sean borrow them for a bit, they could be dumped. Stuff like for example Saitek Brute Force, or CXG Legend/Concerto.