Spiral Sash Balancing System

Hi, I recently bought a townhome and a couple of windows show broken spiral sash balances. The sashes would not stay up. I was able to remove the spiral balance, but not the plastic casing where the balance goes through as the window is not removable. The metal part of the balance is 30 inches, 3/8" wide and the hole on top is 2/8" approx. The balance is in very poor condition (rusted). I was able to see the plastic part (white) which I attached a picture. I think I need an entire replacement of the system, not only the balances but the springs and plastic casings. The spiral was actually just laying at the bottom of the window frame which makes me think it had no tension and it was not attached to the sash. Can you please tell me exactly what part I need to order to reproduce the system please? Thanks.