As far as I know, Secret Oktober is only available on the Union of the Snake 12" Single. One of their many great b-sides. They really need to release all of their b-sides on CD. I've had to make my own.
BTW, a new remastered version of RIO is being released in a few weeks. Can't wait for that.
Not much of a difference, but "Secret Oktober" was also available as a b-side to the "Union Of The Snake" 7" single, not just the 12".
It was never released commercially on any collection. It's always been one of my favorites from Duran Duran. A shame it hasn't had an official CD release on any compilation. Maybe since the original 5 members are regrouping, a b-side collection will follow.