Imperial HiFi are now UK stockists for the Topwing Seiryu Blue Dragon and Suzaku Red Sparrow coreless straight flux cartridges.

You can read a review of the Seiryu Blue Dragon here:

https://www.monoandstereo.com/2017/12/topwing-blue-dragon-up-cartridge-review.html

Topwing Seiryu Blue Dragon Cartridge Topwing Suzaku Red Sparrow Cartridge