where to buy the best video for CPR training?

I would suggest that you consult with the American Heart Association. The website is http://www.americanheart.org . The guidelines were very recently changed, so it is important that you make sure you are getting a newly updated video. (I was trained this summer, and then re-certified last week under the new guidelines. My CPR class watched the new video, so I know there is one.)

CPR/First Aid Training

You should go to this specific link: http://americanheart.org/presenter.jhtml?identifier=3011764 which is the CPR section of the AHA's website. This should provide you with the appropriate information as it depends on the type of certification you need. For example, CPR training materials differ from the type used for students and the type used for medical professionals. I don't know exactly what you need, so this is probably your best bet to start.

Good luck!