I don't know what happened to the outfit that sold The Knee Pod but I've used one for 15 years and it works very well. It kind of snaps over your leg ahead of your knee and is adjustable in height. I've used it sitting flat on the ground, on archery type tripods, and on stand like you describe. It seems the rails are always too low.
I googled it and didn't find much but some have been sold on ebay.