To the best of my knowledge, there is no online resource for tracking down previous owners and the WBCCI would not be inclined to disclose member information, especially to non-members or info on past members.
However, if you are a WBCCI member, you receive a Membership Directory annually. If they are still members with a newer trailer, they may have transfered their membership numbers to their new trailer and could be listed...or they could have been reassigned. Obviously, if they are no longer members they wouldn't be listed in the current directory. In that case, you may be able to find an older directory from someone who has been a long-term member which may have a listing of your previous owners. Of course, if it's been a while, their info may be outdated....
Good luck on your search!