This site only pulls listings off of the MLS. Why are you interested in by owner? Is it because the type of property you are looking for does not exist, or is it because you are hoping for a steal of a price?
Inventory comes out a few different ways. Regular listings, pocket listings (listings agents know about that are not live yet), and for sale by owner. If there is a specific subdivision you are looking for (The Coves, The Glen, etc) then you can also solicit homeowners directly.
If you are using an agent in the area, they can get this done for you.
Broker Baird & Warner