Sometimes some of the vendors have affiliate pages where they have some videos or graphics you can use. Otherwise its all hard work from scratch! If there is no obvious link on the sales pages for affiliates, then write to the vendor and ask if they have an affiliate page (most vendors put an affiliates page link at the very bottom).
More effort = more rewards (usually!)
Get your camcorder out, make your own video review, write your own unique review/articles, etc.