This is an interesting question. As an agency we’ve tried to hire someone in PR that has a network for link building, I feel like they don’t exist. Everyone in PR is focused on media business and doesn’t relate enough to links and an outreach plan for them. Also, the practice of pushing out a release on Prnewswire or something similar to earn links has faded away in recent years.

Reality is, you want to create content for your client or yourself that is unique and link worthy, of its good enough for industry people to push out, reach out to them yourself.

Someone else may know a PR agency that focuses on link building, I haven’t come across one in 5+ years.