Even if you find new paneling, it won't match, simply because of age and exposure your existing paneling has. Colors might be close, but never match. (kind of like replacing shingles on the roof of your house, new ones never match the old ones, if they are from the same stock and have been stored away).
Best suggestion as donn0128 suggest. Replace with new and somehow incorporate that into the design of the RV so it looks like it belong, if that be paint or some other creative design.
If you have kids, you could replace and paint it was chaulk board paint. Now wouldn't the kids have fun with that! :B