Just a suggestion from my experience Gaza
There is usually a sales office on site. Get talking to the sales people (usually saleswomen/estate agent reps) in there, they will definitely know who ok's getting the showhome windows done, and they are the ones who sell the houses so they'll be giving new owners the welcome pack.
I made up flyers just for such occasions in the past. With a personal welcome to the new owner, hoping that they settle into their new home, and without sounding too presumptuous letting them know I'm the window cleaner for their estate, so they won't have to worry about looking for one. One less thing to worry about as they settle in. All nice and friendly.
Hope something of use there
Regards Pj