I have some black sand substrate and river rock if anyone is interested.
Tahitan black sand + marine black sand mix:
Should be enough to give about 2 inches in a 10G. Would ship in a medium or large flat rate box, depending on whether I can cram it in a medium box.
Smooth large river rocks:
Polished and coated. Enough to fill a medium or large flat rate box (I need to check which, I will if someone expresses interest in it).