One option is to generate a PGP Public Key is via command-line. Here is one tutorial:
Another option is to install the Mac software at https://gpgtools.org. A useful tutorial after you install is at http://support.gpgtools.org/kb/how-to/first-steps-where-do-i-start-where-do-i-begin-setup-gpgtools-create-a-new-key-your-first-encrypted-mail. You may need to export or email your PGP Public Key to yourself and then open it in a text editor / word processor to copy it. You can find the key fingerprint in the Details area of GPG Keychain application after you’ve created your key.