soprano ligatures
It depends on how much money you want to spend and what sound you're after.
I was using a Rovner dark that also fits my Selmer hard rubber (soprano) mouthpieces.
Just recently I bought the (two screw metal, Paris, France) Selmer ligature that fits my (alto) Selmer scroll shank metal mouthpiece. It costed me $24.
If you want something cheaper a standard two screw ligature that fits soprano hard rubber pieces will probably work.