I made an effort to try and find it, and honestly it's entrance hides in plain sight. (down in the main levels where all the shops and stores are. A staff worker in the mall gave me a hint because I was getting to the point I was going to start gnawing my arm off.
It basically looks like corridor that utility/janitorial and other mall staff would use...then as you wander down the corridor you start to notice pictures on the wall of celebs etc. Then it opens up into a small pizza spot.
@Boris Zubov indicated it can be hit or miss, I lucked out that both visits for me were awesome.
edit: or google can help you really pinpoint it
I will make a concerted effort to visit this place whenever I return to Sin City! Thank you for that!