Ideally there would be, perhaps with a spec where one could put key fingerprints in tag field for easy searching.
Discussion
What would be your main usecase for needing someone to use this pgp key.
I’d agree the social graph formed in nostr is a nice way to share it. But Nostr is already a key pair, what functionality do you tap into by incorporating an additional pgp/gpg one.
Encrypted email?
Yes encrypted email or plaintext messages and verifying software integrity - something I am not sure nostr keys are quite ready to do yet.