As MIck says ^^, you're unlikely to find anything pre-built, 26" is not far off as obsolete as 650c! Especially 26" rim brake with a 9sp hub...
Something like this would work though:
https://hollandbikeshop.com/en-gb/bicyc ... spokes-14/
and then a cheap set of Shimano hubs, eg:
https://www.chainreactioncycles.com/shi ... prod155153 (says 10sp but it'll work with 9sp with a spacer).
Or you could go one level lower and get Sora for about £30 which is already 9sp.
Just make sure you get the same number of spoke holes for hub and rim!
And then take them to a friendly local bike shop and get them to build them up (or do it yourself if you feel you can).
The size difference is about an extra 6mm of drop in the brakes. Do double check the tyre clearances when you fit a bigger / wider tyre. The slightly smaller rim size should mean it fits OK but some 650c frames, being designed for racing and triathlon, have paper thin clearances between frame and tyre.
Smallest 26" tyre you're likely to be able to buy (easily...) is about 1.3" so I'd be checking that will fit before buying new rims and hubs!
