Very happy to help, I can send you the most current listings for both 2-families and duplexes. I am a Trulia recommended agent who is very familiar with the Pioneer Valley market. Just click on the Contact button...Thanks!
If you live in the Springfield area, you may want to go into a couple broker offices and meet a couple agents to find the best one for you.
If you simply want to do the house searching yourself, then looking on Trulia, http://www.zillow.com or even Realtor.com would probably give you a pretty complete list of what is out there.
Let me know if I can help!