In all honesty, I don't think you would like a 30 round magazine. I've owned them and used them. I didn't care for them, nor did anyone else that I've dealt with.
Pros - holds 30 rounds
Cons - heavy, costly, tough to load, don't fit magazine pouches/cases, unergonomic, unreliable.
You can get +3 baseplates for the SD9 magazines though.