I use a jumbo "tea strainer"; works great.

Strainers and colanders with different-sized holes will work.

I don't have any plans, but they don't look like they'd be too difficult to make. I currently use the top of a large shoe box as a tray to clean seeds, along with 2 different sized strainers, and my pasta colander. Just regular kitchen stuff. I've collected a lot of seed this fall and have been able to clean almost all of them using this hodge podge of tools.

I fantasize about getting a nice matching set of screens and tray(s) to clean seeds though.