The 4473's aren't filed by the buyer's name, but by the date of disposition. Compiling a database from that would be random, laborious, and full of holes.
That's only about a two week job at best to scan and compile them into a fully searchable and indexed database.
OCR software is nothing short of awesome in it's degree of sophistication these days.
As far as the job of actually scanning the forms in goes, that's child's play.
Just look at the sheer bulk of "documents" the US Post office scans.
There's very few technological barriers any more when it come to data gathering, data manipulation, data storage and data retrieval.