Most large grocery stores, such as Walmart, have it. Some of the smaller ones have it as well, but you're more likely to find it where there is a bigger variety of things.
As for where to find it, it usually can be located where the other bigger bottled juices are. It usually does not come in the normal small bottles or juice boxes.
in my fridge. It tastes atrocious :((( I got mine at market basket...im not sure if they have those outside of New England tho...
Any big store, or you can buy grapefruit and squeeze your own(: Fresh is the best!
most big stores sell it, look around the lemon-aid.
grocery store and small shops like healthy options