Odd size window balance

We live in a 20+ year old community. Everyone is having trouble with the windows and it has to do with the balances. Retired from construction, I could help with repairing them. I have changed them when I was working. The problem is that the length of the balances is longer then what you have in your stock. The length I need is 28 1/2 (or 5/8) inch as you can see in the picture. the diameter is 5/8" (9/16).         I hope you can help with the problem.                                                                                                               Thank you,                                                                                                                                                      Andrew