I agree with Joe Bodeck - the MLS is a great place to find lease option deals. But in my experience, the MLS is better for finding "sandwich lease option" deals - where you are going to stay in the middle. Whenever there is a Realtor involved, it's a lot harder to explain to them that you are going to "wholesale" your lease option to someone else.
When I do talk to a Realtor (and they are a great source of lease option leads), I always approach the conversation as though I am an investor looking for a house to lease purchase for myself. If the numbers work, I will stay in the middle. If they don't work, I will sell my contract to someone else.
If I am talking to the Realtor of the house I want to lease purchase, whatever commission they get is between them and the seller. It's none of my business. I just make the offer.
But really - if you are looking for lease options to assign or flip - Craigslist is the best place to go.
I look in the "For Rent" and the "For Sale By Owner" section. I then send a text message, a voice mail, and an email asking them if they would consider selling their house on a lease purchase. I only call back the ones who respond.
In my opinion, cold calls work - but only as long as someone else is doing them. It can get very frustrating & old, really quick.
In addition to Craigslist, there are 2 other strategies you can use to find motivated sellers who might be open to a lease option:
1) Call all the wholesalers in your area. Ask them what they do with their "trash leads" - all the leads they throw away because they have little to no equity. Tell them you will give them 25% - 50% of your profit if they send these leads to you and you do a lease option on them.
2) Look in Zillow for all the new "For Rent" houses in your favorite zip codes. Then look up the owner's address in the county records, and send them a simple "we buy houses" yellow letter. I am getting a 20% response rate right now doing that. Think about it - these are houses that have been vacant for at least 2-3 months. A lot of these sellers are tired landlords. If they aren't looking to sell, they might be looking to buy more properties. You can add them to your cash buyer's list.
Hope that helps!