Common problem, just clean up and lubricate the rails, job done. If you are looking for another roof a scrappy would be your best bet although your more than likely have the same problem with them, if you want new you could try Ford as said it's the same as any other model, but I doubt they will have them, indeed they have very little parts wise for these cars, although I know these still sell seals etc so it's worth a shot. Also look for Carparts-Express (Trader on here) as they specialize in Ford parts.

Martin