SRAM compatible 11 speed 12-25 cassette?
You should read Zinn's articles (a, b, c, probably others) on 11 speed drivetrain compatibility. 

The surprising upshot is this: You can swap a Campagnolo 11 speed, Shimano 11 speed and SRAM 11 speed wheel in for each other and they will work (*). You can put SRAM and Shimano cassettes on each other's freehub bodies. 

The Shimano Ultegra CS-6800 comes in a 12-13-14-15-16-17-18-19-21-23-25, so this is a cassette you can buy and use. 

(*) Zinn notes there might be a tiny amount of indexing adjustment necessary. The SRAM/Shimano swap for wheels isn't really surprising, but the Campagnolo one is.