Usually any do it yourself place, if they have pool supplies and chemicals they should have sand (#20 silica sand). Pool places have them to. Id grab 10 bags for ya but I havent worked with pools for 3 years now.
At one point I did sand with a snapping turtle and 1 goldfish
You can use the sand over and over, unless you suck some out when you gravel vac like I do with my very fine gravel, then just replace some.... all this talk about sand makes me want to change mine out.. Please stop!