Atrium 26-3 LX CMC 11 Balance Replacement

I need a replacement part number for an Atrium 26-3 LX CMC 11 balance with a channel length of 27". I also need the part number for the plastic stop that attaches to the top left inside channel of the window but there is a 5 photo limit so I will submit it on another post.

Here is additional photo of the balance along with the photos of the stop. The stop measures 2 3/16" long, 5/8" wide for the lower part, 13/32" wide for the upper part, 1 7/16" long for the lower part and 3/4" long for the upper part.