The lost manuscript of the full text of Eusebius’ Gospel problems and solutions was last seen in Sicily five centuries ago. But it could quite possibly still be there.
It might be nice to search for Sicilian mss. I was thinking about it last night. We have a couple of clues. Latino Latini writes that Sirleto had seen the ms. in Sicily.
1. We need to work out what Cardinal Sirleto was doing in Sicily, and where he was doing it. A study of his life should provide clues, and possibly his correspondence is extant (published would be nice, but improbable). This might tell us where he found the ms.
2. We need to work out what collections of Greek mss exist in Sicily, and also which were taken elsewhere (to Naples? to Spain?) An enquiry of specialists like N.G.Wilson should provide clues. Are there Greek abbeys there?
3. We know (how) that Aurispa sent a shipment of Greek patristic mss from Constantinople to Sicily a century earlier. Why to Sicily? Where to? Where might they have ended up? Is this one?
Once we know the answers to these, and have a list of search sites, then it becomes a question of looking in catalogues, and visiting collections.
Might be an interesting project!