Who supplies the frozen granite or marble for ice cream parlors?

I am opening an store that, as a part of its service, makes and sells ice cream with add-in or mix-ins, whichever you call it. I understand the stones (granite or marble) are frozen from below by condensers, or freezing mechanisms. Does anyone know where I can find one? Who manufactures them? I have having a hard time finding them and my equipment dealer doesn't seem to know, either. Any help would be great. Thanks.