"Law Enforcement" has no interest in this at all. I've proposed such a database around and had absolutely no interest shown.
Here in California, I've asked the police about how to check numbers & they will only do it if you first buy the gun and then bring it in.
If anyone has some idea of how to setup such an online database, contact me and maybe I'll set one up.
I've also proposed a law be passed in every state with some kind of enhancement for stealing a gun & knowingly buying / selling a stolen gun. That's the only gun law that would actually help with "crime guns". However, that's not the objective of politicians so they don't care. They are only after honest people.