Here's the website where it's available: http://www.corvettegadgetman.com/products3.html
It's designed to either sit on the lift cup of the jack, or remove that and bolt it onto the floorjack frame using an adapter. The adapter didn't fit on my jack, so I took a round piece of steel that fits inside the cup and keeps it steady:
http://i162.photobucket.com/albums/t248/hcbph/Corvette/Shop%20Tools/IM001954_zpse192ca67.jpg
http://i162.photobucket.com/albums/t248/hcbph/Corvette/Shop%20Tools/IM001953_zpse192ca67.jpg
The other thing in my pictures is a tool I designed to assist in taking out old u-joints without risking bending the yoke if it's corroded or there's a burr present.