Wish I could have found more -- I did searches for type "F" belts, but only got typical tooth belt catalogs for the usual versions -- XL etc.
He did mention re-gearing his lathe to accept conventional belts.
I wonder if, though obsolete here, whether the F type belts (.1875 pitch) may still be manufactured in China for their domestic use in older style machines? Maybe an online marketplace like Alibaba might turn up something...