One method of reaching out to node providers that could be helpful is to search their name here on the forum and then scan all the hits. Sometimes links to their posts can be found in reviews of Node Admin, Participant Management, or Subnet Management proposals that are posted by members of the CodeGov team, the CO.DALTA team, or the Aviate Labs team. Usually those reviews occur shortly after the node provider posts their declaration or onboarding statements, so they often know where to look and will document it in their reviews.
Another method is to look up the node provider in the wiki link below. This will provide a link where you can join a small chat group with each individual node provider and Dfinity. Some node providers are good about checking the matrix channel on a regular basis and some are not.
The final recommendation I can make is to reach out to Katie Peters. She seems to do a great job of keeping track of who is who in the node provider community and may know their username.
By the way, I learned all of this within the last week while trying to help @borovan with his investigation posted here. Our reviewers at CodeGov have known how to perform this research for a while since they review proposals, but I haven’t had a need to do the research myself until recently.
I hope this helps. If you think there is an improvement that can be made to how to reach node providers or what quality of information they should submit, then you can certainly start a conversation making a suggestion. I think everyone would like to see improvements in the work process.