The Pepsi corporation ownes some fast food chains in the US, so you're not going to find Coca-Cola at a Taco Bell for example. Aside from that, I've never really had trouble finding Coca-Cola in any kind of restaurant. Then again, I don't usually look.
I think coke and pepsi try for exclusive arrangements at every dispensary. That means most restaurants prefer a discount from say pepsi for exclusivity, than to offer both with reduced profits.
