For the Advantage module, just put a favorite search on eBay, but I would recommend against buying from Coburlin unless you have more money than you know what to do with. He has "Buy it now" prices for Advantage modules at $300 and optical wands for $500 and I'm sure only the people who haven't been looking around buy from him. He publically said on one of the forums that HP calculator enthusiasts were idiots and he would take advantage of them-- or something like that (I don't remember exact words). If you're patient, you'll do a lot better.
I don't know what to suggest for the hinged cover.
The manuals can be gotten on CD at http://www.hp41.org/ArchiveDVD.cfm