Beorn's people, if they were the same folk whom the Wargs and Orcs were going to raid in THE HOBBIT, may have come from Mirkwood south of the Old Forest Road.

That would explain the connection between the Beornings and the Woodmen of Mirkwood without requiring that a third group exist south of the Beornings and north of Lothlorien (although there is no reason why they couldn't be there -- but Tolkien doesn't explicitly mention any).

So, I would list the Men of Rhovanion at the end of the Third Age thusly:

1. The Beornings, living on both sides of Anduin
   
   
   
2. The Woodmen of southern Mirkwood, living near the forest's western borders
   
   
   
3. The Woodmen of northern Mirkwood, living near the forest's eastern borders
   
   
   
4. The Men of Laketown and Dale, apparently indistinguishable at the end of the age
   
   
   
5. The Men of Celduin south of Esgaroth, said to be akin to the Laketowners
   

This is pretty much what I show in Parma Endorion, I think. But these are all attested groups. No speculation.

Michael
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Parma Endorion: Essays On Middle-earth