The HP67u is a microcode emulator for a HP67 calculator. It is a close as I have been able to get to the real thing.

HP-67 Owners Handbook and Programming Guide
Saving Magnetic Cards
HP67u Credits
HP67u Disclaimer

Sample HP-67 programs
Convert HP-67 keycodes to keynames (“31 25 11” -> “f LBL A”).

Eric Smith’s HP-67/97 Hex Table
HP-67 Internals Reference
HP-67 Internals Articles