It has to be a 12-30 10 speed casssette or can you make do with a 12-28?
https://www.universalcycles.com/shop...2&category=534
If you have to have 12-30 then it's available in the higher price point Ultegra CS-6700
https://www.universalcycles.com/shop...4&category=534
Other brands too. But this isn't filtered for Shimano compatibility.......
https://www.universalcycles.com/shop...p?category=534