The largest LCD 4:3 is 21.3 inch, but these are very expensive, but is has 55mm more vertical height than a 21.5 inch FullHD display!
The largest 4:3 image can be had with a 27 inch 16:10 LCD, which has a 24 inch 4:3 image (probably rougly the same as CRT's were not always measured to true image size). I have a 27 inch 1920x1200 in my cab.