If all else fails, place a For Sale By Owner Sign in the front yard. If the owner is in the area or any neighbors know the owner, they will probably call them. When the phone rings you can build your buyers list and if the owner does call you, your response can be some to the effect of, I'm sorry, did my staff place my sign in the wrong yard? Do you have a house for sale or is this home for sale?
The worse that can happen is you build your buyers list
Good luck
Tim