Thanks for the feedback, guys.  I don't think the client has any inclination to contact their existing developer or even knowledge who built their site!  Guess to some people websites just aren't THAT important!  If the consensus is that there's no way to de-list their old site, then I'll have to insist they do make contact!

Thanks again!

Hi Search Experts!

We are just launching a new site for a client with a completely new URL.  The client can not provide any access details for their existing site.  Any ideas how can we get the existing site de-indexed from Google?

Thanks guys!