@dschallock
not sure about the 68K version, but LyleHaze would probably know since he was in contact with alfred. you could try sending him a PM in case he doesn't see this thread.
-- eliyahu
I'd be happy to answer any questions, except it looks like all the info is here already.
The last commercial 68k version was 2.5b (I think). I think it's available from Alfreds site.
Alfred developed it further for many years, and also created versions specific to MOS and AmigaOS.
After Alfred retired from further B&P work, I asked for, and was granted, the AmigaOS version for further development.
(shameless plug) AmigaOS versions 4.1FE and onward include a complete 16 channel General Midi softsynth in the "Contributions". Using this, external synthesizers and MIDI interfaces are no longer required.