How to find a RE agent for residential income property?

[Mark Hu]

I've been searching for a real estate agent to help me find a duplex or triplex for sale. I would like a buyers agent, and one who has at least been involved some transactions with residential income property.
How can I search the internet for these requirements? For example, I was wondering if on trulia or zillow one could find out what agents were involved in recent sales of duplexes or triplexes.

Thanks