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Might these be any use to you? Rigid a Grizzly carbide £50 from SJS https://www.sjscycles.co.uk/rims-tape/rigida-grizzly-26-559-mtb-css-rim-black-32-hole/
Or https://www.ebay.co.uk/itm/Hope-Ti-Glide-Retro-Silver-XC-Mavic-CD-CERAMIC-26-Bike-Wheelset-Wheels-Titanium/323572905983?hash=item4b5672b7ff:g:hPUAAOSwj81bqmBb
Spendy as but reflecting the fact 559 ceramic rims are rarer than 700C these days
Here's another carbide rim if it might work for you and built on to a nice Halo hub https://www.ebay.co.uk/itm/Rigida-X-Cel-Pro-Carbide-like-Mavic-Ceramic-Rim-26-front-wheel-Halo-Hub-720g/202532767769?hash=item2f27e4c819:g:sq4AAOSwR5BbC9Z3Have you put a wanted ad on the MTB section of retrobikes?
luck hunting
Be quick
https://www.ebay.co.uk/itm/Mavic-D521-rims-on-Shimano-XT-Hubs/223271854111?hash=item33fc0a201f:g:GOwAAOSwUPVb4xb-
Hopefully the rims aren't too worn out for you...