Jefa will make you one if you give them the dimensions, although it'll probably cost more than that (but their roller bearings are very good). Beware of the 25% Danish VAT.
Or if you're happy with a simple (non-roller) bearing, any good workshop with a lathe can turn you one from POM stock (aka acetal, Delrin).
On my boat, the lower bearing was seized in the housing, but the upper bearing totally fine, so I only needed to replace one. Very happy with my Jefa rollers.