Schuro and Thel in germany used to sell them but stopped a few months ago.
Now Thel is offering their own series of "conductive plastic"-pots in a black box.
It´s very odd indeed that no one is able to say why you can´t get them anymore.
Might be worth contacting Panasonic directly.
Maybe they were to exclusive/expensive for the (consumer)-market?
When I think about it, the non-selected ones (matched to 1dB difference) were "only" 20€.
They are quite good indeed; although not much superior in comparison with even an Alps RK27112. The only Panasonic plastic pot I own is sitting in an amp I built for my brother. Maybe I should sneek in and exchange it?