Contacting the appropriate people shouldn't be too hard. A lot of websites out there are selling lists of company contact information or you can also going directly to the company websites and navigate to their "broker network" or "vendor signup" links. Actaully getting registered with each of those companies is some work but absolutely required. I think you're on the right track.
When you start registering with BPO companies, asset managers, or lending institutions you're quickly going to find that some companies that want to charge you an initial or monthly fee to be on their "preferred broker" list. I would be VERY cautious about doing this. There are just too many companies you can sign up with for free.
If you consistently complete BPOs and (appropriately) promote your name on each one, good things should start to happen.
PS: It took me about 25 completed BPOs before I was offered my first shot at an REO listing.
Hope this helps!