If you want a Confederate battle flag there are lots of places you can buy one. If you feel they aren't available enough to your liking you are free to make one or even start selling them yourself.

Walmart making a business decision to stop selling something that is racist has nothing to do with freedom of speech. It would also be a poor business decision to start selling ISIS flags, Nazi symbolism, those racist figurines that were once popular, a holocaust reenactment video game, KKK robes, or any other merchandise that divides their customer base. So what?

Part of freedom is the freedom to choose what you do and don't sell.