Interior help with lost part.

Hello
I am finally getting my 68 Plymouth Barracuda back together. Finding and losing parts as I go. I habe came to a dilemma and need a little help.
Right below the rear sail panel there is a plastic piece. It holds the upper interior metal piece for the rear quarter window. I don't know the name of it or I wouldn't ask. Not sure if I can buy one or someone has one. But I am in need if anyone could help me out would be quite grateful. Thanks