The nearest Apple/Best Buy (they have those great-deal cards) store is like 30 minutes away from me (I wont commute that far for just a couple cards), but what other stores sell $50 cards? Do places like Vons or CVS sell $50 cards?
Where do you not buy iTunes cards is a better question. In my area even gas stations are selling them now. You'd be surprised, look wherever your local convenient store has their phone cards and/or other gift cards.
I know. Everywhere has iTunes card. I recommend Walmart, because, well, Walmart is amazing. Who doesn't love Walmart? I would LIVE in a Walmart.
Wal-Marts by me have always been really trashy, but they just opened a new Super Wal-Mart that has a food/produce section that is absolutely out of this world. I can't believe it's Wal-Mart when I shop there.