Cat flap with tunnel extender - help!

[Florence4170]

I need to fit a couple of cat flaps into quite deep walls. I have heard of a cat flap where the extender is cut to fit rather than 50mm deep bits which clip together. Please can anyone help with suggestions for these? I can’t see any on Amazon or Pets at Home.

When we had our kitchen extended I couldn't find what youre looking for. I had to use 50cm extensions, then sealed it with silicone sealant as wasn't a perfect fit. Will follow this thread though incase someone has the solution.