Spindle drive belts?

Has anyone found a source for the Sherline V drive belts when
needing other sizes for modified drives?
The stock belt is MB-330 (Mitsuboshi). 6mm wide x 330 mm inside length.
A loooooong search on the web turned up nothing but the MB corp site.
Are there any USA distributors?
I have found a MB-280 belt at a sewing/vacuum repair store (now closed),
but I would like to see the whole line catalog.
McMaster, Gates, Berg, SDP, etc have nothing close.
An alternative is round urethane heat joined belt, but the whip at high
speed is a loser.
The MB belts are perfect for this application. Strong & flexible.
RichD