I'm confused about what you are trying to do. Do you need an 8-speed, 9-speed, or 10-speed cassette? What kind of shifters are you using? The difference between most 10-speed and 9-speed cassettes is the 16.
I've converted all but one of my 9-speed Shimano cassettes to start with 13 tooth cogs and include 16 tooth cogs. In the past I've been able to buy 16t cogs from Sheldon Brown and there are other sources. Some of the Shimano 9-speed mountain bike cassettes have individual 16t cogs that can be added to a road cassette. My favorite 9-speed cassette is a 13-26, most of the cogs are from a lightly used 12-34 XTR cassette that was gathering dust in my garage.

Al