Glass polish is available from restoration specialists.(try Frosts). It comes as a reddish powder which is mixed with water and applied as a paste with a drill mounted hard buffer. It's made in part with diamond granules as far as I know. It works but takes ages, gets very hot, and spits the cutting paste everywhere so paintwork needs masking. I used it on my MGB and it was a reasonable result, but thats all.
Rain X do a glass polish - a white cream, but I doubt it will shift any scratches that you can feel.
Rain X water repellant won't do much in my experience.
