That microwave was manufactured for Dometic by LG Electronics. Unfortunately, appliances, like cars and trucks are changed from year to year. Trying to find "that particular microwave" which was made in 2007 would be similar to trying to find a "new, never sold" 2007 car or truck. Dealerships just aren't going to have one on hand. It's possible that an RV parts store "might" be able to locate one for you, or at least a similar sized replacement.
You might also check "RV salvage yards" for one. They are "junk yards" (if you will) for RV's and those types of businesses make their money buying, disassembling and selling "used parts", usually at a discount. There are several listed in the "RV Parts Sticky" located here:
http://www.keystonerv.org/forums/showthread.php?t=12986
Have you considered removing your existing microwave, taking it to an appliance repair center to see if they might be able to repair it? If not repairable and you can't find a replacement of the same model, you might be faced with rebuilding/modifying that space and installing a replacement. There are several available with "shroud kits" to allow you to adapt them to almost any application. The end result is similar to what you'd see in most "current model RV's"....
Good Luck