Slider window

I’m trying to identify and replace a plastic roller used on a horizontal sliding window. The roller is located at the bottom of the window sash and allows the window to slide left and right.
 
The wheel sits on top of a raised metal rail that runs inside the window frame housing. The roller has a groove in the center so it stays aligned on the rail and does not slide side to side. It appears to be made of plastic/nylon and is part of the bottom window assembly.
 
The window can be lifted slightly to remove it from the track for servicing, and the roller fits snugly inside the lower sash channel.