FYI with Kalium, I wanted a tapered low B .130(?) for my 30” scale bass. They only offered it as a “guitar” string with guitar ball ends. I threaded a ball end from another bass string over the kalium and it was able to catch on the guitar ball end and work fine on my bridge.
This strategy might work for our OP here for the upper strings - find guitar strings with enough winding length, and use bass ball ends to hold them in the bridge. The lower 4 strings can be a short scale bass set.