It's really not hard to find Mexican Coke made with cane sugar, it's the price that's off-putting. Even my local Kroger (I live in a small town in a rural area) has mexican coke in the mexican food section of the store. It's $1.99 for a single bottle, but since I only drink one or two a month, that's not a problem.

You can also go into just about any little hole in the wall mexican grocery store (we have several in my area) and find it, usually cheaper.

Take a look around your town, I am sure you will find some. ^
(and stay away from HFCS, it's the devil! lol)