Here's a recent thread about sourcing them in the UK https://guineapigcages.com/forum/showthread.php?t=4394 and another https://guineapigcages.com/forum/showthread.php?t=4556.
Good luck, it's such a pain they're so hard to get hold of over here.
Good luck, it's such a pain they're so hard to get hold of over here.