Identify and purchase 4 balances

I am trying to locate and purchase 4 of these. I believe it is some kind of balance. 29" long. All windows are vinyl. Frames and windows with thermo pane double glass. upper window is fixed not movable. Lower window has two slide latches at top of frame near the outer frame that when slid retract the pin that holds the top of window in frame, window can tilt forward and come out of the shoes at the bottom and be removed completely. Pin at the bottom of window fits in shoe that is part of mechanism that i sent picture of. Kitchen window is 29 long by 33 1/2 wide both top and bottom sections. First bedroom 29 long by 33 1/2 wide top and bottom. Next bedroom 35 long by 33 1/2 wide top and bottom. Have looked for mfr and model but not there.