1. Are you asking how to find stock video of waves and frozen rivers? Search relevant terms at any stock video agency and be prepared to discover 100,000's of options.
2. You're interested in buying and using a stock video, but not clear how to make a color video black and white?
3. You're interested in buying and using a stock video, but not clear how to resize it?
I would suggest hiring a professional to do whatever job you're thinking about doing.