There's a picture on page 5 of this brochure that shows it. Definitely not the greatest mattress. We actually had an extra ordered when we got our rig since I, too, was worried about finding a replacement if anything happened to the original.
The air pump takes FOREVER to inflate the thing. We bought another one (haven't used it yet), which will hopefully be an improvement. Come to think of it, anything will likely be an improvement!
If you haven't tried already, I would definitely give Coachmen a call to see if they can send you a spare mattress. If not, my couch is made by Mastercraft (and looks like the one in the brochure pictures). Maybe a call over there might help you locate another one: Mastercraft, Inc., Innovation and Value since 1971
Hope this helps! And, hope you're liking your rig!