I think that there are a number of specialist agencies that work with
HR people however the level of service you will get depends on the relationships formed with the consultant that you get. Like any business, their service is only as good as the person you deal with (even though some agencies will have more integrity than others).
Where are you based? Perhaps if you advise the forum where you are located, people can share the names of people they would recommend in your region.
If you are in Qld, I would be happy to share the names and details of people I have worked with and found to be very good operators.