Where can I download a database of RSA keys? I'm looking to do some research into how RSA is used in the wild. I've read through a few papers and it seems other researchers have had no trouble collecting millions of keys to perform analysis on.

I've done some preliminary research but can't seem to find any one site from which to download other people's public keys.

I assume that given the nature of public keys that it would not be a privacy risk to have this sort of database available to the public.
If RSA keys in PGP format are fine, you can download them from any keyserver.

Many keyservers, at least MIT, have a robots.txt that disallows automated downloads, so be sure to check that before attempting to bulk download anything.

If you need a large collection, you could download a keyserver dump and filter out what you need.