Just because you call Newmar doesn't obligate you to buy the part from them. Are you sure the glass has a decal or is it etched in the glass? You could either buy a kit and do the etching yourself or take the door to a glass shop and have them do it.
Tempered glass can be etched, it can even be carved, as long as you don't go too deep into the surface. Carving can weaken the glass and make it prone to breaking more easily.
If it's acrylic, you could mask the clear area and use fine emery cloth to 'etch' the pattern you'd like.
Trying to match the other panels might be more difficult than creating a new design on the door. A mountain, tree, Dutch Star, etc. might be appropriate.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI