And I would like to correct the previous post, in New Jersey all real estate commissions, including rental commissions, are negotiable. While it is true that, in most instances, the tenant will be asked to pay the commission on a rental, that is negotiable and you can always ask the landlord to pay the whole or part of the commission. And the landlord has the right to say "no", still you will never know if you don't ask.
Definitely contact a local realtor and find a good attorney who can ensure your rights to purchase a rental property are completely protected in the lease/purchase agreement.
The best places to find rent to buy opportunities are the same places you would look to purchase any property, including Trulia, the local Multiple Listing Service and Realtor.com. In this market, I would ask landlords if they would entertain such an arrangement whether or not it is offered outright. Many owners today are renting because the market is depressed and they simply want to wait until it improves to sell. Therefore, many will consider rent to own situations whether or not they thought of it themselves.
Good Luck and feel free to contact me here through Trulia if I can be of further assistance.