There are no specific ranges of figures for Rhovanion, the Northmen, Dale, and Laketown.

With that said, those cultures are closely related to the Rohirrim.  My Rohirrim figures are a mix of historical plastics, and figures originally from the Games Workshop LOTR skirmish game ("Middle Earth Strategy Battle Game").  The GW/MESBG figures are great.  A wide variety of historical ranges in plastics will mix well with them in 28mm scale.  Dark Ages cavalry and infantry figures in mail and in clothing work well. Carolingian Knights, for example; anything pre-Norman.  Norman Knights in mail are fine if outfitted with round shields (which appear multiple times in Tolkien's descriptions of the Rohirrim) rather than kite shields.

The MESBG Rohirrim figures do not have a lot of variety in their infantry, so I supplemented with a bunch of Dark Ages plastic infantry figures with roundshields.  Figures in mail work well for Guard infantry; without mail for militia.  Anglo-Saxons and Viking figures are very good; Rus figures with a bit of Eastern/Russian flair are nice as well.  The more pointed helmets are nice to distinguish Esgaroth and Dale from the more generic Dark Ages forces of Rhovanion.