I was actually looking for it today! I found it on the 88th floor, right in front of the lift. If it doesn't appear, just use that way stone next to you. When you zap back to the 79th floor, use the way stone again to get back to the 88th floor. If it's still not there, just repeat zapping back and forth until it shows up. It's a lot faster than warping down and running back up. At first, I thought that's what I had to do, but it's more simple than that. Good Luck! It took me four tries with the way stone!

~Glitch