Two things: be sure you know the difference between a lease with option and a lease purchase and 2. In a buyers' market where prices are on the decline, I don't think a lease option/purchase is a good deal. You will have to come to an agreement on the price today, but don't know what the value will be when your lease is up and you need to proceed with your option or worse, your purchase.
Some properties listed in MLS do have notation indicating that the seller will consider a lease/option.
An agent can pull data for you that identifies this status. Additionally, a cross reference of properties which are offered both for sale and for lease are possible opportunities for lease/options.
I am not aware of any comprehensive and accurate source for lease/options. There is a site for OwnerWillCarry.com, but I know little about it and pass that along for "info only" and am unable to recommend it.