One method of obtaining karrikins is to collect smoke from a fire and pass it into water. However, higher amounts of karrikins remain on the char.
A simple method is to burn some dry plant material containing cellulose in a metal can, and before all the material is consumed, to smother the fire with a lid. After cooling, the lid is removed and some water is added. The solution can be decanted or filtered through a coffee filter. The solution is then applied to the seeds.
Smoke products used for seasoning of food are available in the grocery but they contain extra ingredients which may have an inhibitory effect on seed germination.