Hello Elizabeth.  While I know of no classes specifically aimed at the
musical box repairman (or woman!), I think that you could benefit from
classes in clock repair, as most of the things in a musical box can
also be found in a clock.  If there are no classes nearby, I'd suggest
a few books which would give you a good feel for the processes, tools,
and materials needed, particularly those tools and processes necessary
for working with mainsprings, which can be quite dangerous if mishandled.

I'd suggest: "The Clock Repair Primer" and "The Clock Repair First
Reader", both by Philip Balcomb, and available from many booksellers
Also "This Old Clock", by David Goodman, and available from the author
who can be contacted at <dsgood@worldnet.att.net>

These books don't cover the actual comb or pin barrel, but will help
you with other parts of the musical box mechanism.  Good luck!

Regards,
Bob Loesch