Used to be Faygo vending machines near me. Don't see them anymore but many stores still have those bottles anyway. I was never much into Faygo otherwise (remember it more for it being cheaply used by schools as refreshements during open houses).
I get it at small markets/gas station convenience stores usually. Many of them will carry the 24 oz bottles. I tend to avoid the larger 2-liter ones because they're so big. Most of the grocery stores I know tend to carry those over the smaller ones, unfortunately. The one grocery store seems to carry 24-ounce bottles of diet flavors only, but the grocery store that is the closest to my house sometimes sells 3 of the little cans for $1 on the clearance shelf in the back. It's often rather picked over, so I have to dig through a ton of diet ones and Ohana iced tea, but for me it's worth the effort to find the good ones.
It can vary where I am, a close convenient store I go to has both the 24 oz. bottles and the 2 liter ones, but hardly anything in "Diet" though (not too big on that corn syrup aftertaste lately). The local Dollar Tree used to get in Shasta 2 liters but has since changed over to Faygo (both are owned by the same company these days).
Not a fan of HFCS aftertaste, so I tend to favor diet sodas.
Oh if only I had begged my mom for some Barq's when they pulled this stunt!
I don't think my state will ever repeal theirs.
