3M colorquartz is available in black as well, S grade is a fine very smooth sand.
http://solutions.3m.com/wps/portal/3M/en_US/ColorQuartz/HomePage/Products/Crystals/ to see if there is a distributor near you click the link (where to buy) in the top right and select your state. Price seems rather variable. I almost bought the S grade black but was just to hard / costly to acquire for me.
I've been curious about the flourite black sand myself, as I am debating switching to it. But I wonder how abrasive it is? I too would need a smoother sand, but I havent really looked into the flourite enough to know how smooth it is. If you dont have plants, I'd at least look into if you can get ahold of ColorQuartz though.