Maybe you could use the moulds for round bath bombs and then join them together with a little melted soap.Another way that might work is with an icecube tray that l have,it makes small round balls similar to the way you use a 3D mould,not sure how hard the balls would be to get out of the mould but since the mould is flexible it shouldn't be too hard.
Sometimes I let a little extra soap stay in my melting pot,as it cools and becomes semi soft I just peel it away from the sides and just start forming it into a ball then I just dip it into whats left at the bottom and add to my ball if I want to. 8)