Hi - Not quite sure what you mean by the middle part but - I got the top rail part from Custom and Commercial - perfect replacement for the LHD one I have which has a couple of cracks.
Try this page to see if they have what you want.
http://www.customandcommercial.com/products.aspx?sub_category=1764&category=212&group=61" onclick="window.open(this.href);return false;