Originally Posted by
Sixty Fiver
Shimano offers a 14-25 9 speed cassette which is a very practical cassette to use... it tightens things up across the middle quite nicely.
In theory one should be able to easily buy Shimano cassette cogs and from those, build whatever cassette you need or replace cogs that wear faster... this would probably cut into their profits though.
I can't say about Shimano and Campy, but
AFAIK for SRAM you can't buy the unified block that ends with fewer teeth than 14 or the two loose end cogs in anything other than 11, 12, and 13. Also the two end cogs are position specific I think, so a few other loose cog choices would be necessary to have a 13-26 or 13-30.