If you know when it was deleted, you should be able to find the last-pushed hashes in https://www.gharchive.org/, and then can likely still fetch those hashes via any surviving fork - even if it doesn't look up-to-date (since github commingles the actual pack storage underneath forks).
If you know when it was deleted, you should be able to find the last-pushed hashes in https://www.gharchive.org/, and then can likely still fetch those hashes via any surviving fork - even if it doesn't look up-to-date (since github commingles the actual pack storage underneath forks).