I've bought the Niagara non-aerosol spray starch at both WalMart and Target. Before that I bought an aerosol brand at WM. RIght now I'm using diluted Staflo Concentrated Liquid Starch (in an empty Niagara bottle) that I also bought at WM.
The first time I bought starch at WM I needed to search through the laundry aisle; now I know where to look (bottom shelf), but I'm not sure what's around it.