How to find bird-doggers nationwide?

Are there professional bird-dogs in each market?
Are there national bird-doggers or is the idea that a bird-dogger only finds “hot” leads?
Do they only get paid if the lead turns into a sale?

I do bird dogging in NC (also property inspections for out of towners). Most investors pay by lead. Some ask for just the location with certain requirements and others want additional information on each property such as owner’s name.