Funnily enough I was looking into something similar for my TT bike to take to Norseman. In particular I wanted 12-30 for Shimano freehub, which Shimano themselves don't do in 11 speed.

I bought a Miche cassette. These guys will make you up a custom cassette from sprockets of your choosing, as long as you don't ask for something silly.

UK but ship to US.

https://thecycleclinic.co.uk/...es-for-shimano-sram#

Cheers, Rich.