The Coke models, like the Hummer (there are 9 in total) are available from independantly owned convenience stores (Giant Eagle, Quick Check etc), either as a free gift with purchases of Coke (20oz bottles, multican etc....), or can sometimes be sold seperately (often around the $4 mark). Each store has a different promotional plan for them, so what one store does is not necessarily what another does.
Large places like Walmart, Target, Kmart etc are not doing the promotion.