What cassette remover tool I should order for Shimano CS-HG50?
All Shimano cassettes, and all SRAM cassettes other than "XD" ones, have the same spline pattern.  If you search for "cassette lockring tool" you will find lots of compatible tools.  Virtually the only incompatible ones will be SRAM XD and Campagnolo, and they will be specifically labeled as such.