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Evolution is where i got mine from but alternative auto would be another good one. Along with bamachips and brenspeed. There are more but those are the most common ones you hear of.
With the SCT xcal2, you have a choice of three tunes, plus stock. So you get a choice of 3 octanes. Mine has 87, 93, and 93 Extreme (from Evolution Perf), and I run the 93E in my daily driver.