Submariner needs help!

I am a pitcher and I converted to throwing exclusively sidearm & submarine 2 years ago. I currently throw 2 kinds of fastballs and 2 kinds of sliders. I need help coming up with another pitch. I was thinking a change-up or a sinker. I do not throw hard. I am having trouble finding any sites or books that cater to submariners. Anyone have any tips for an aspiring Dan Quisenberry? I am 30 years old and play/manage several amateur teams in New Jersey.