How do I determine who the listing agent is?

[Holly Scott]

I get listings from a realtor I have worked with on my last flip. But I have no way of seeing who the listing agent is. Sometimes she is not able to get me info right away (I am not her only client:) and I would like to start making offers directly to the selling agent when necessary. How do I get this info? When I search the listing online I get many different realty sites but no way to tell who is the listing office