I tried the Mr. E, and it seems to have all the "top notes" of old-fashioned cola, but lacks the underlying flavor - it's more like those old cola lip balms that they used to sell. I've also tried Pep-C from PV Liquid, but it was all the bottom end flavor, with no brightness. I tried blending them, to no avail.
I also tried the Cherry Cola from TV, and it's good, but they add cinnamon (just a guess) to give the fizz, and I think it overwhelms the rest a bit. I've also ordered a custom Lime/Cola from them, and it should get here tomorrow.
Still looking...