Hi PineRidge,
Agri Supply also has them. On my sprayer, a ball valve is screwed into the bottom of the tank and the filter is connected to the valve. I found that when cleaning up the rig after spraying, it is convenient to remove the filter "cup" to allow the water to drain faster from the tank. While I have it off, I can check for debris in the screen and flush it out if needed. The filter mesh screens come in various sizes, and I am not sure what to advise you on that one. The screen is finer than window screen.
HTH
-Vinnie