Double hung window Identification

We purchased a home in upstate NY near the Canadian border a few years ago. The house was remodeled in the mid to late 1980's and new windows were installed in the bedrooms. The windows are all metal with insulated glass. They have a wood cap over the interior of the sashes that is removed by removing two screws on the top of the stile and 4 screws in the plastic handles at the bottom. Removing the wood reveals plastic sliding (vertical) parts about 1" wide extending the full height of the sash. Removing 4 flat head machine screws allows the plastic to slide off and the sash to be removed. The glass is held in the metal frame by machine screws also. The balances for the sash consists of a miniature block and tackle system with a lower two pulley block riveted to the lower part of the sash and the upper two pulley block connected to a spring. A heavy duty braded nylon string about 1/8" in diameter connects to the center of the fixed side. The pulley blocks are about 3/8" wide and 5/8" high. The rivets have bulled through the lower block on both the left and right side and the sash will not stay in place.
There are no identifying manufacturer marks on the windows and the builder is not available.
Does anyone have any information on the manufacturer these windows or where I could obtain parts?
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