available at drugstore, but search for root cause
crankin, it is TYPICALLY used as a protective layer to prevent further blistering on feet by hikers. you can get it at a drugstore or sporting goods,
but... i would try to find what is causing the "stratching". is it to the window itself, or to a tint film that was applied later? if film, i would go to a GOOD tinting service and have them find the root cause of the problem. if it is film, it is most likely already ruined and should be removed or replaced. a GOOD tint shop will warranty their work, and will eliminate the problem before reapplying or not offer to do the job. a GOOD tint job will be approx $200-$300.
good luck. - benton