You might contact Swift Canoe of Canada, as that looks a lot like the seat I have in my Pack 13.6. You can check out their current pick of their High Back Seat with Lumbar Support, at https://swiftcanoe.com/boat/pack-13-6/#specs-section
My thought would be to ask Swift where they are getting these seats, or if they have them to sell.
In the alternative, call up North Star and if Bear has deigned to return from Alaska, offer to ply him and the crew with IPA's for information on the same.
Best of luck with obtaining the right seating, and what wonderful craft you have with which to ply the waters.