a fist full of cash.
not many 4:3 LCD's exist anymore....let alone larger than 19 inches. by the time LCD hit that size, everyone made the move to widescreen.
lots of 16:9 monitors have a 4:3 option you can set in the settings to keep it from stretching video.
just buy a 27" wide 16:9 monitor with this feature that will fit and mask off the sides on the glass to retain the center.
otherwise, you are looking at having a custom one off panel made...and it ain't cheap. I think some dudes here where looking at having custom cut LCD digital marquees made (can't find the thread sorry
) and where looking at a huge pile of cash to have even a small handful made.