Usually before you start an affiliate program, you would want to have some track record of sales so that affiliates know the potential of the product.
Knowing only what you have written above, I have jotted down some ideas for you. Of course, you will need to decide what is right for your business.
If you are still in the early stages, I would try to connect with some networks or organisations focusing on real estate agents. Go and meet them or connect by phone and ask them to do an article in their newsletter or review your app for their members. This will give you some exposure, hopefully some sales and definitely some feedback about how it is being received in the marketplace.
You need to find out how your target market likes to be sold to before investing lots of resources in one particular method. Being real estate agents, my hunch is that they would prefer face to face or phone contact rather than digital.
Another option could be to hire someone with experience in the real estate industry to sell on a commission basis for you. Of course, that would depend on what the price and margins of the app are.
Also, think about the future of your business (not just this one app.) What kind of company are you trying to build? How do you want it to look? What kind of resources, contacts and networks do you need to be building up now?