where can i c this DL?
Daryl teaches it on his Ambitious card routine. It does require a get-ready. It just uses a left thumb count to get the break. Some magicians like this DL, but it is basically a slightly flourishy strike-like double. I think it is fairly hard to make it look decent.
I don't know what Sankey was teaching, but I know that he has done a basic strike double which does not require a get-ready.
I think one of the best, and reasonably easy push-off double, is the Vernon Push-Off. It does require a get-ready, but there are many ways to get ready in a logical manner. The advantage to the Vernon Push-Off is that you push the top card to the right with the left thumb in the center of the card. That is more natural than from the edge.