Reach the enduser

Any tips from anyone out there to try and find the enduser on a domain? I havn't had any luck yet.

One thing I've done in the past from time to time when having a regional name domain name (like londonhotels.whatever, for example) is contact travel businesses in those areas by email and let them know that it is for sale and then give them a date (usually 2 weeks in the future) that it is going up for open auction where anyone can bid on it. I usually contact them by email. Sometimes it works and sometimes it doesn't.