Don't wind the roof back if it is too stuck, or you'll jump a tooth and damage the bowden cable.
You won't find replacement cable anywhere. I fixed mine and lubracated the internal cable and external runners. I had it completely apart as the cable got mangled.
I have a spare roof I bought a few years ago, it is seized but you could break down for glass or cables if you wanted, or fit seized shut if yours is stuck open like mine was!
Also have a rear motor in working order.