Write them a nice note saying that you were in the area and saw what ever it was you saw and did the research to find out who owns it because you would love th be able to buy it. Be over the top enthusiastic so they think they are going to make a killing by calling you back. The sellers need to believe that you will do anything, pay any price, to get your hands on the property or they won't bother to call. Once you get them to call you then arrange to meet them at the property and be ready to discuss terms.
Do all that you can to get them to mention a figure first. Then be fair and maybe give a little to make it a win win. You can have an attorney write up contracts or if both you and the seller walk back iinto one of the real estate offices I bet you'd get more interest