Where the hell did you get that?

Oh that would be top secret or... just a PM away ;)
EDIT: Please note (came in my mind later to specify about it) that it was NOT obtained in an illegal way.

is that the real ACOG or replica? I'm sure its real, well 80%.

You can be sure 100% now, it's real ;)

EDIT: However, a new replica is coming out from G&P, and it's the replica of the scope you saw up above on my M4, that is, an Acog TA31F exact copy:

http://www.gp-web.com/en/productspop.php?pid=832

As you can see, it is incredibly well made.
Naturally the fiberoptics on the replica won't work (i.e., you won't have the lit red arrow inside) and the red tube on it is just a dummy but still, I find it hard to tell between the real one and this new replica.