Go to Turfco.com and check out the booklet "Why Aerate My Lawn" or call Turfco at 800-679-8201 and have them send you some. They are made just for what you want and will also fit in a letter envelope.
Here is a little tip that works...Take their little booklet or one you make...Put a personal note on the back like "Hi my name is so&so and I will aerate your lawn for $50 and sign it" Put this in a door hanger bag you can get at an office supply store and put in a plug from the lawn. This works...The trick is to do one lawn in the neighbor hood and hang these on the neighbors doors...Also make up signs to put in the lawn "Aerated by Your Name"" Finally, Aerate the sidewalk to street several times so there are tons of cores so the neighbors see them. All these little tools work.