Watch American Diggers, Rick Savage has excellent cold call skills! Then meld that with some Billy Mays, a little used car salesmanship and bring beer!
Maybe that's why I really suck at cold calls....
Start a database of everyone you know or are related to. Find out who lives in older homes. Work with people you know first and you will get more comfortable brining up the subject. I hunt a lot of sidewalk tearups in older parts of town. I make conversation with anyone who's curious about what I'm doing and give them some history of the neighborhood in case they were not aware of it.
When people think you are actually into the history of the area, not just the raw pursuit of goodies, they will often invite you to hunt their yards. Started one very old yard hunt today just through the current work in the neighborhood and a passing conversation with the guy who lives there.
I pointed out the history of his house and it's age, all of which he was aware of but the fact that I took the time to learn about the block-by-block history of the area made him very comfortable giving me the okay to come by anytime.
Some of the other properties nearby, I am waiting to catch the homeowners outside and walk up and make casual conversation. Yeah, sounds like stalking. It is in a sense. But not a real creepy sense. Always carry a couple finds from the neighborhood to show and tell because that really gets the homeowners attention as well. But it's because I am really bad at cold calls or at least that's what my history of cold calls tells me.
Always remember you are asking someone to let you enter their yard, dig up things from their yard, and keep things you dig up from their yard. Is that something you would let someone else do at your home? Especially if they came knocking at your door while you were watching American Idol and grilling salmon?