There are many ways to find prospective domain buyer(s). One way is by using the feature available from Valuate.Com. Let me explain how…
If you have the domain, for example WhateverYouSay.Com, and you are interested to find out whether this domain name has any prospective buyers, you can follow this method:
1. Go to Valuate.Com
2. Put the domain names with all extensions (com,net and org) and press "Valuate"

3. When the result comes out, it is shown that the (dot)Net name has been taken. Now find out who owns it by clicking the Domain Tools button (marked by the red circle)

4. Unfortunately for this name, it appears that the owner is using the private registration to hide his/her contact info (shown as "Domain By Proxy" as the registrant, this is the private registration service by GoDaddy)

Well since for this particular domain name we cannot find the actual owner, you can apply this method to find out the potential buyer for other domain name(s) you wish to sell.
Good luck!