Need to Replace Broken Channels in MW Vinyl Windows.

We have MW Vinyl Windows installed in our home that was built in the year 2000. Many of the window channel balances have broken at the top where there was a plastic piece that fit into an approximately 1/4" square hole. I don't think these balances are manufactured any longer and we are looking to replace them with a comparable channel balance. We have single hung windows. The measurements are as follows:
Lower window sash: Height 30 1/4 " and Width 32 3/4"
Visible window glass lower window sash: Height 27 1/8" and Width 29 13/16"
Lower window sash weight: 18.6 pounds
Total window including vinyl framing: Height 60 1/2" and Width 34 1/2"
Pivot bar portion that slides into window: 2 1/2"
Pivot bar portion that sticks out of window 5/8"
T Shape Shoe: Height 1 1/2" and Width 1 1/4", narrow stem is 1/2" wide
Channel length: 28 1/2" long

Thank you for your advice on what parts I will need to replace the entire channel.

Yes, the spring is a 1/2" in diameter. Since the mounting piece at the top of the channel is plastic and snaps into a 1/2" square hole, instead of screwing in with a screw, what should I use instead. Thank you.