In Baltimore the only place to get belts is Baynesville Electronics. My
perfect phone machine needed one or two belts every 5 or 8 years, and it
was worth paying whatever was charged.
IIRC, their belt display is not what it used to be, but I'm sure
everything is available by mail, that is, on the web. The display may
have had a reference book saying what things used what model belt, but I
had to go buy dimensions instead. If not exact, get the shorter one.
They probably stretch quite a bit but they don't get shorter.