Are there any existing open source implementations of "id-tied" public/private key encryption?
What you're looking for is probably Identity-Based Encryption (IBE).
I'm not sure if I've got the terminology correct, but here's a few concept with IBE.
IBE has a key generation center that has a function equivalent to a CA. The key generation center manages a master private key for deriving private keys for decryption users, and a master public key for which encryption users to derive the public keys corresponding to the decryption users.
The rest is pretty much the same with other public-key encryption: encryption users encrypt their messages with the public key of the decryption users and send the ciphertext to them; the decryption users decrypt the message with the private key they've obtained from the key generation center.
It is to be noted that there is the obvious problem of key escrow and difficulty with revoking exposed private keys.
China has developed the SM9 identity-based cryptography standard. An English version is available at IACR. The official version is in Chinese, and is behind paywall, some provincial administration publish free links to Baidu Netdisk file sharing service.
The OpenSSL fork GmSSL mentioned in the comment, has appears to be the most comprehensive implementations of Chinese commercial cryptography standards.