Need replacement balance

The window balance measures 30x1/2 x 5/8 not counting the plastic parts at both ends. I think something snapped off the plastic part pictured. The other end is intact. The window is a series 5000 TMF AAMA/NWWDA 101/I.S. 2-97 with a further identifier of H-C30-54x96. However, this is not the dimension of the window. The visible window glass on the bottom half of the window frame is 29x30 1/2.

I'd like to purchase two replacement parts if they are available.

Thanks.