1960's Window Slide

I have some windows from the early 1960's (~1963) that are void of any manufacture marks - I have pulled them out, looked 360 at the frame and windows for any marks - none. These windows open outward, on a plastic sliding mechanism that is tensioned by a spring at the top of the window and supported by an arm at each side of the window. Over the years the plastic slide mechanisms have wore-out and/or broke and I am in need of replacement slides. Any idea as to the what they are? The nipple of the part has a spring slide over it, and the spring and part fit into a channel at the top of the window where they are tensioned by a set screw. The base of the part fits in a channel of the window frame and slides up and down.