Bucket Seat repair help

I have a set of bucket seats in my Dart that I was told came out of a late 70s Cordoba. Problem is the seat tracks are loose. I took the drivers side a part first and found that the plastic "H" pieces that hold the roller bearings in place and take up the slack in the tracks is shot. Does anyone know how to repair these or better yet, where can I get these pieces. I went to the Dodge dealer and they do not show the parts in the parts manual. Any suggestions?