Finding a replacement will be difficult. I suggest looking at eBay for a used one, otherwise you will have to find a substitute. Since the door speakers are 2 Ohms, even a substitute may not work well if it isn't 2 Ohms as well. If nothing else, you can replace both door speakers with 3.2 Ohm versions, but then you will have to offset the Fade control to keep the sound balanced front-to-rear.
Take a chance on this one maybe (?) should be the same part: http://www.ebay.com/itm/1993-2002-Po...3D361564086257
By the way, under no circumstances try to peal off the screen from the front of the speaker or you will destroy it. Examine the speaker only from the back or by carefully cutting away the screen with a razor blade.