On top of that, I'm looking for the Steam Version.
Civ 5 is a Steamworks game, which means no matter where or how you get it, you have to use Steam to play it. If the copy is a physical CD then you have to enter your CD key into Steam. If it's a 3rd party digital copy, you still have to activate it on Steam.
That said, I can gift it to you for 4 BTC.
Civ V is a Steamworks game, but OnLive is a Cloud game service. When you buy an OnLive game, you don't own it, or even the rights to use it. What you own is the right to play it on their servers using their cloud technology. Buying from OnLive means you have to use the OnLive player, you can't play offline, and you can't play multiplayer with non-OnLive users (about that last one, that's true for most games, idk about Civ V).
Edit: Civ V on OnLive isn't multiplayer at all.