Call the news desk of a news agency. You can find most news agencies' contact details on the Internet or from directory assistance.
Offer your footage to the news desk and ask how much they are willing to pay for it. Explain what you have a footage of, how long the footage is and how you acquired the footage.
Walk up to a journalist at the scene of the disaster or accident if you cannot find the news agencies' telephone number. Offer to show your footage and ask how much the journalist's agency would be willing to pay for it. Agree on a price and provide a copy of the footage.