I bought an Excursion last December to use for an engine swap. It wasn't rebuildable, but it certainly took a lot of work to strip it all down. Hopefully the actual swap will be done in the near future.
I used Insurance Auto Auctions to find mine, even though I was also watching Copart. They are the two big names in the industry, and IAA typically has more of a selection of Sunlines. They aren't all that great though- most have to be pretty far damaged in order to get on there. Fires, floods, etc. With a stick built trailer, there isn't much good left from a flood trailer, and a rollover one would need a total rebuild if it had good appliances and cabinets from a light roll. The best way to rebuild a Sunline is to either find it damaged privately or happen to find one like the above that jackknifed or had something minor. Usually a jackknife situation ends in much worse though.