A while back someone asked where they can find guarana soda. They have it in two-liter bottles at El Cubano Food Bag Market, 11350 Victory Blvd at Tujunga in the San Fernando Valley, (818) 506-0911. There's another branch at Sherman Way and Tujunga that I haven't been to.
The brand they have is one I've never heard of. It's "Brazilia" brand. Although it has a map of Brazil on the label and says "The Best From Brazil", it never actually says that it's imported from Brazil. Nor do I recognize it from Brazil. It does say in the list of ingredients, "carbonated water, sugar and/or corn sweetener, imported guarana natural flavors, citric acid, caramel color, preserved with benzoate of soda", from which you can draw your own conclusions.
Anyway, the El Cubano market is a good place. They're cheap and they have hot tomales for sale at the checkstands, along with multiple brands of annatto seed paste and other necessities.