No markings on the window
Hey! We can't offer the spring, unfortunately. Really, only millworks still handle those jamb liner springs. As for the clip, though, we do sell it. Check out 20-022!
No, we don't handle those types of springs any longer. You would be hard-pressed to find a spring on its own that works, because the spring would need to be calibrated within a few pounds for your particular window. It's possible that you might, but I would think you could only find the right spring by dumb luck, and I wouldn't count on that.
No, a spiral balance won't replace your spring. Your only option is to contact a local mill work and have them replace your jamb liner. I am sorry we cannot offer an easier solution.