The rubber for the belly band is an off-the-rack purchase at any Rv parts store/website.
Per trailer-specific parts:
That one's tough since the trailer's been out of production for years. Is the rear window missing altogether?
parts may be available from Trilliumrv,
since the Surfside's based on the Trillium
and they do carry some replacementparts for early trailers....post some pics of what you're looking for (especially rear window) and we may have more suggestions.
sells exact duplicate door hinges for the Trillium
brand, but I think Surfside
used something different from those used on the Trillium. As I recall, though, Surfside also used refrigerator
hinges and they're probably still available at websites that sell such things