Did you try asking the alternator vendor?
In any case, to guesstimate a part number you can try this:
Let's say you have a 2014 (IDK what year you have or whether or not you have A/C), and the part number is K061015.
06 is the number of ribs = 6
1015 is the length in inches = 101.5
Subtract .5 inches from 101.5 = 101
The new part number would be K061010.
Search for the part, then check the manufactures published specs against the stock belt specs to make sure it's what you want, and adjust again if needed.
Hope this helps.