I think what @Bill Coleman said is absolutely right. Find a/some "seasoned" agent(s) who has a lot of connections in the RE investment world and they'll be able to help you out. I'm up front with them and tell them that I'm working with multiple agents who are contacting me if they are finding deals and most of them are ok with that. I also tell them that I'm especially interested in deals that aren't on the MLS... yet....
Also, some wholesalers (at least in my area) come across deals that will be seller financed, I've found a few deals this way.
Ultimately I think the best way is to start networking and entrenching yourself into your local RE investment "world." I haven't set up a deal through this method yet but there are a few people that I now know who are looking to exit the landlord business in a few years who will potentially be wanting to sell their properties but still maintain some sort of cash flow. I'd get to know these people on a personal level so that you are aware of what they are planning to do (REIA groups, landlord clubs, etc.). Perhaps they will come to you first when they are ready to sell and I think it's easier to enter into a transaction with people who you already know and trust.
