Christine & James,
To maximize your chances of finding a home that offers one of these, you need to first locate a Realtor who works in the area where you want to buy.
The Realtor will have access to all listings in the local Multiple Listing Service (MLS). At any given time, there are usually only a small number of homes for sale with a Seller willing to offer either owner financing or a lease with an option to buy.
You can find an agent in your area right here on Trulia. Just go to the bar at the top of the screen and put in the city and state, and type of professional you're looking for, and press the "magnifying glass" icon to bring up a list of people who can help you. Good luck with your property search.