Window balance and other parts needed

I have some single hung aluminum windows made by a company called Alenco. They are about 18 years old and some of the balances appear to be failing. One, in particular, will not hold the window up. Others are very difficult to open. In addition, some of the pins that stick into the balances have broken off and some of the clips/releases at the top of the lower sash that releases the window so it can be removed have also broken. One window in particular (see pictures) is the one that won't stay open and has the broken parts. That window is part of a twin and the individual sash is 33.5" wide by 30" tall. I'm unable to find any model numbers on the balance or on the window. What additional information will you need in order for me to find the proper parts? Thanks!

Thank you!