Old fashioned size bars on my road bike – 26.0 clamp size (and on all my other bikes). Would like to get one of the cheap simple bar mounts like this but all the ones I’m finding seem to be for 31.8 bars. Am I missing something, or is anybody successfully using one of these with spacers to suit smaller bars?

Yes. Using the pair of spacers from an old light bracket. Hope i think.
Have seen someone use the spacers from a multi fit front mech (with a little trimming)

Thanks – have shimmed plenty of other things, looks like the obvious solution.

Exposure brackets come with 31.8-25.4 hard shims.

Might be available as a spare.