hi Ian
I actually meant posting a wanted ad for the shim, I am sure you will have no trouble finding a USE post. The posts are all 25.0mm, few are 27, so you will need to find the right size shim, a 26.4mm one. The good thing is if ever you change bikes you can just buy a shim to fit that frame and use the same post.
Hope this helps.
Thank you for thatPlenty of 25mm USE shims available on sjs cycles website.
https://www.sjscycles.co.uk/seat-posts/254-use-seat-post-shim-aluminium-250-mm-id/