Ah, that sucks. I hate to say it, but 4:3 large LCDs were only available for a short time, were tremendously expensive, and *MUCH* lower in quality than the CRTs. The best one was the SyncMaster 240T by Samsung, and it was $9,999 new. Hard to find on the used market, but the color accuracy, response time, viewing angles are all atrocious compared to CRTs or modern LCDs. The 240T is 5 years old now. 20" is the largest commercially available 4:3 size still out there, and they're somewhat rare. Is desk space a huge issue? Two of these would provide exceptional quality for cheap :
Ebay 21" QXGA CRT
Failing that, you can buy a new 20-21" 4:3 LCD, or scour for a used obsolete larger 4:3 LCD (not recommended, they will be outrageously expensive, poor in quality, and a disaster if anything breaks on them, which is pretty common with older LCD monitors with the power board, inverter board, and vga boards being the primary culprits).
What is the application? Maybe there is a workaround for a wide aspect.