Look on line for a wrecking yard that may have a one from a crashed car, state the color of trim you want. Looking on line you better your chances of finding a replacement unit rather than confining your search to the Boston area. Call or visit your Mitsubishi dealer (perhaps it is inexpensive) so you have an idea of cost. You may need the Vehicle Identification Number (VIN) It is about 16 or 17 numbers long and can be found on your vehicle title, lower corner of the front windscreen, or door jamb.
Shocking price! Have you tried on line. Just a quick look http://www.msrecycling.com/ http://www.usedpartslive.com/live/1/year/MITSUBISHI/ theirs loads more hopefully someone has the lamp your looking for.