Google has a new Dataset Search tool. It looks good.
An initial test search for Krita (the open source paint software) didn’t pick up anything, so it is just limited to datasets and is not also bringing in general file-names from FTP servers.
A wide search for Antarctica Cephalopods then gave a good set of 25 results, all of which were record pages that appeared to place their dataset under CC or to be public domain (NASA etc). There doesn’t appear to be any way to then load a further set of results, or to do a further keyword search within the record-pages of the results.