I'm not sure that a publically downloadable database is available, but I think you can talk to DrHyde if they want to share the http://deps.cpantesters.org database with you.

Personally, I would just look at CPAN::Mini::Visit to visit each of the latest distributions of a CPAN mirror and extract the needed prerequisites. Alternatively, you can visit each distribution and home it has recent/accurate META.json files and use these to build your dependency graph. Also, maybe CPAN::Mini::Visit::Simple actually is simpler or simplyfies the job at hand.