You might put together a good offer, find out the name of asset manager, and submit the written offer directly to the asset manager. Chances are slim, but making a direct approach with a healthy deposit might pull it off. Find a title company to hold deposit, or better yet, state in offer binder due one day after acceptance. Keep in mind the asset managers have no experience in selling a property, which is why they rely on getting it listed when the time is right.
My firm is a preferred Realtor for some of the major bank's foreclosed properties. If you are a cash buyer, I can let you know what inventory I have inspected and have under management that have yet to hit the market. Or I can send you a list of current foreclosures and give you the pros and cons of short sales vs. foreclosed properties. Richard