To anyone looking to replace a comb, I've got good news and bad news:

The good news: A disc playing machine often can have the comb replaced.
A single comb is relatively easy to replace, a double comb may need
tuning to match the combs, but in general it is possible.

The bad news: Cylinder musical boxes are not standardized.  The chances
of finding a replacement comb is like trying to find a missing piece of
a jigsaw puzzle from a different box -- it might fit, but the picture
would be wrong.

Do not despair, there is good news: A combs is repairable; if it is
economically feasible is another question.  You can replace individual
teeth, blocks of teeth and, if only the thin tip of the tooth is
missing, that's not a difficult thing to replace.  What's the catch?
It all needs tuning afterwards and it's very expensive.

Additionally, a comb that has had that much damage likely also needs to
have the cylinder re-pinned -- another major expense.  Without measuring
the comb and cylinder, it looks as if your customer's musical box needs
around $1500 to $2000 worth of repairs.  Is it worthwhile to them for
sentimental reasons?  Let them decide what to do.

I will not go into the details of replacing teeth here, but if you would
like a description, look in Ord-Hume's works on the subject or contact
me personally; I will be happy to describe what is done.

Best regards,
Eliyahu Shahar