General (main property discussion here) - Contacting landlords?

I am a landlord myself and am planning of going into lettings in my area as I think I have something better to offer. How can I get in contact with willing landlords to do some market research? Approaching other agencies is obviously not viable as they would be right in thinking I'm stepping on their toes. Are there any sites or sources where landlord information is held or where landlords advertise properties privately?