I've seen some of my competitors do some great PBN campaigns (at least majestic.com think they're great campaigns) but obviously it is tough to tell who owns the PBN so I can reach out to the same vendors. I'm pretty sure they're paid PBNs (as opposed to the competitors owning them) because other sites are on them. Anyone know any tricks to tracking that back to the vendor who owns it? Domain whois was a dead end. Contact form on the site didn't help.
If you are able to find the owner of a PBN then the owner is not doing a very good job of hiding their footprints. Keep that in mind. However, if you ask around to various SEO's you may be able to use their services, which they almost certainly have at least one PBN.
You can try sending an email to the email of the WHOIS even if it has privacy enabled. Most of the privacy services forward the email to the registrant. Also you should look for contact forms on the website. If the owner has built his PBN right, he should be able to receive that message from the contact form.