The TX39XX series processors are based upon Toshiba's TX39H 32-bit RISC cores. There are actually 3 cores: TX39H, TX39H+ and TX39H2. These have mostly been utilized in printers, copiers and PDAs like the Philips Nino and Velo.
According NetBSD/hpcmips, The Sharp Mobilon HC-4600 uses a 74MHz TX3912. Maybe it is compatible.