Another part of the answer to the first question:
Yes, you can do a fishless cycle in a bucket of sand. Part of the problem is that there is not a lot of oxygen lower in the sand, and when you move it to the tank you may not have the higher bacteria population at the top of the substrate.
Suggestion: Do the fishless cycle in a shallow container, perhaps a plastic storage box, and only use 1/4 of the sand.
When you set up the new system put the non-cycled stuff in first, then put the cycled sand on top.
Where to find black sand:
1) Eco Complete is a good planted aquarium substrate that looks like black sand. Coarser, though.
2) Tahitian Moon Sand is very expensive, but is absolutely black.
3) Swimming pool product by Pebble Tek is added to the finish inside a pool to make it any color you want. It is fine quartz bits. Completely aquarium safe as long as you avoid the product line that has real sea shells in it. Mostly blended colors, so the black might actually be about 75% black blended with whites and greys.
4) Try brick or masonry yards. Some may have something that will work for you.