Howdy Bunch,
I am looking for 28T Shimano HG cogs, in 9 or 10 speed. Five years ago I could find 'em; I used to order Miche compatibles from one of the UK shops. I remove the 2nd-position cog on a 13-25, or a 12-25, as the 13s are out of production, and put the 28 in 9th position.
If you have one to spare, let me know. I could probably harvest a 28 from another Shimano cassette, but I'd rather not buy an entire cassette for the one cog.
All best & thanks!
BC