Eastwood and Amazon have windshield glass polishing kits listed, no first hand experience here though. Amazon usually has more reviews & ratings than anyone else.
One trick I learned this winter that did wonders for my old back glass that I thought I was going to have to polish was spray cleaner (fantastic or 409) applied liberally and then gone over firmly with a new single edge razor blade, almost like your shaving the glass. Got a lot of baked on crud/film/haze off, went over both sides a couple times and glass came out so nice I forgot about polishing.
I wouldn't apply any polishing compound before doing a thorough cleaning like this.
