You'd be surprised what you can find on eBay. I got some decent velcro bed-cuffs for not a lot of money.
They do look awesome. If you find them anywhere, let us know yeah?
The problem with portability is evidenced in the GIF you used - Even those "heavy duty" stocks are being moved by the lee's legs. Unless you're going to find some way to weight or clamp them down, there's a safety hazard.
For a modest amount if money, you could build some yourself. You could make them exactly as you want. It’s not a difficult project. There are also free blueprints online if you feel you need help