|You won't find them in the shops, but you can still buy them online. There's a choice of 4:3 monitors here: http://www.ebuyer.com/search?page=1...|
Use Google Search to find more online vendors. Just type 4:3 monitors as the search criteria.
Widescreen is much more popular now, and so much better suited for modern Windows applications. I would advise you to get one instead of the old 4:3 format (unless your graphics adapter doesn't have any widescreen resolutions to choose from).