From about 1973 until 1979, James Wayne in Victoria, TX. was the Darne importer, and R10s, R15s, and V19s were stocked. Everything else was custom ordered. On occasion, something special made it into inventory for whatever reason.
I wrote those chapters in the blue book, and they have needed to be updated for almost 20 years. Take them with a grain of salt.

Best,
Ted