I'm not sure if a general MACSbug was ever available. AFAIR Motorola did supply it only to OEM. They even had a special manual for OEM manufacturers regarding the adaption of MACSbug I/O functions and adding new commands (like Apple did for
ES (Exit to Shell) and
RB (ReBoot)). Many of them gave the resulting product a name of their choice. Then again, being the micro computer industry of the 70s, they wouldn't have mind an adoption by anyone.
For example Corvus added it (now spelled MACSBUG 68000) to their Corvus Concept. Or Dual Systems added it as default monitor (here spelled Macsbug) to their CPU/68000 for the S100. Or Omnibyte who offered MACSbug as OB68KMACS for the OB68K1A Multibus CPU (*1,2).
Heck, even Motorola did:
On the MEX68KDM (Mororola 68K Design Module) from 1979, where it was originally designed for, it was called
MBUG, while its later (1983?) incarnation with the MEX68KECB (M68K Educational Computer Board) was named
Tutor. The manual included a reference to the now generalized MACSbugname.
So maybe search for either systems software and have a look for the manual.
Edit: The OP has found the MEX68KECB directory on Bitsavers including Tutor/MACSbug Manuals and Binaries.
*1 - It always amazes me how many various CPUs got glued onto bus systems never ment for them. Like 6502 or 2650 to S100 or NS32k or 68k to Multibus.
*2 - They also offered the more powerfull VERSAbug named OB68KVERSA