I am not sure whether GPG supports more than 1 keyring. Is there standard practice for configuration with 2 keyrings - one for users keys and other for system keys (read only for regular user)? If possible with priority for system keyring, i.e. GPG tries to find a key in system keyring first, then user's. In the same time, if new key is added it goes in user's keyring. I know this can be done with keyring path as command line option but expect keyrings can be defined in configuration file and located automatically. At least, is there default file location for system keyring?
And one additional question - is there new version of PGP (at least for Windows) or only GPG is supported?