Window Parts

I'm trying to identify the part in the pic(s) that I sent. It's an Interlock window. The windows are at least 15 years old. I'm trying to find the plastic pieces that fit on the inside of the window. I think that they attached to the tie bar, but I'm not sure if that is the correct description of the metal bar to which they are attached. They are approximately 3.5 inches long and are held in place by two screws. Please let me know if you have this part in stock or know where I can find them.