Your best OUTBOUND source to find endusers

Hello Domainers!

Time is passing by, and I just want to listen your best suggestions when you need to sell your domains ( outbound ) to the correct end user.

Looking for a whois is harder sometimes, and some free sources came to pay sources in order to find a list to potentional end users.

Which tips/sources/software are you using to reach your end users to sell your domains?
(Free sources preffered)

Thank you in advance.

Your best OUTBOUND source to find endusers