If I can make something I will, instead of buying it. This rest I made a few years ago out of some scrap wood, leather, and channel. Adjustable for height, and arm rest. Cost was zero (although if you don't have the tools, wood,hardware, etc. that would cost you a little). It's currently clamped to my back porch rail. Every handgun I own, from .22 to .45, revolvers and pistols, has been sighted in from this rest.
And no, there are no plans. Y'all have the picture. Figure it out to suit yourself.

