I just listed a pair of pretty rare pair of New Old Stock UKAI PLASTIC FILLED TUBULAR RIMS on eBay. These were original equipment of 1970s Fuji Newest and Finest bikes. I routinely search for vintage tubular rims, and these are the first pair I have ever run across (your experience may vary).
The rims may be viewed at the following eBay auction address or item #110531642890:
Regards,
Kevin Kruger - Grantville, PA USA