As far as I'm aware, there is no way of querying the freedb database on anything other than a whole-disc (i.e. DiscId) basis. I suppose it may be feasible to compute a DiscId from a complete disc-set of mp3 files (assuming that the track lengths are all correct), but I imagine it would be neither simple nor reliable.
The freedb database itself is available for download (albeit at about 140Mb, compressed), so it may be possible to make your own, personal, query engine to do the sort of thing you're after. However, you've then just got a static snapshot of the db, and would have to consider how to keep it synchronised.
With luck, of course, someone will come along and prove me completely wrong...
Bryan.
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Bryan.