These parts are at the top of the window. Looks like they are intended to make it difficult to get the window out of the frame from the outside. They have to be removed to lift the window out.
Dave Sr. from SWISCO responded:
June 18, 2014
We don't have the same part shown in your photo, but we do have some that could work as a substitute. Take a look at our 67-002 and 67-004. I think either one is a good place to start.