Shim sleeves are made . machined, with a 31.8mm (1.25") outside
and what the bar clamp diameter actually is , on the inside..
As a mechanical solution, Then, you can use that specific Nitto made bars that Riv Bike sells as the 'Albastache'
which I assume is replacing the narrower mustache bar with a road bar like .. as you say '23.3' * mm ,
not 7/8".. 22.2mm.
those came in 1" & 26mm center sleeve..
https://www.rivbike.com/collections/...bar-26-0-16244
*they specify
23.8mm bar... (drop bar brake lever clamp). and 26mm center..
'Albatross' is a variant of the upright north road bend and uses 7/8" mtb brake and shifter levers and grips.. ....
a mere 1.6mm diameter difference..
....