The National Association of Realtors has created a new certification, SFR, Short Sale and Foreclosure Resource agent. A graduate of the course will have SFR after his/her name. It is a starting point. Also, look for agents who advertise foreclosures.
I've been around a while, and know of no agents who "specialize in REO" properties. Those of us who are doing business are selling REO's though, and can advise you. See my contact info, and call me today if you are serious.