You won't be able to get one from Amazon or eBay. They're banning its sale on their websites as a show of their righteousness. Though they seem to have no problem flogging Islamic and Nazi flags and other paraphernalia.
So, the some 70 million Americans who still admire the Confederate flag as an honorable symbol of Southern heritage worth preserving will have to go elsewhere. Luboš Motl of The Reference Frame suggests this site in the Czech Republic, for one.