If you need to find elasticity of demand for a product using numbers pulled from the internet, you're not exactly going to find it displayed on a company's website (for a number of reasons, the first being that it wouldn't make sense).
Elasticity of demand essentially asks: "If the price of a product changes by X amount, how much does the demand change by?"
Chronodiver is right, in a sense. Things that people need will often be inelastic. Look at electricity, for example. People need electricity. Even if the price of electricity were to increase, people would not stop buying it. The change in demand would be relatively small.
An elastic good works the opposite way. Take soda, for instance. If the price of soda were to skyrocket, people would stop buying it. They'd opt for cheaper drinks instead. The change in demand would be large relative to the change in price.
Anyway, the way I would go about doing this assignment would be to pick a product; eg cars. See if price affects the demand of cars. Choose a company and a car/model and see if you can find data on how many of that car were sold. Also look up the price of that car on Kelley Blue Book or something. Then choose a different, but similar, car from the same company (or a similar car from a different company) and look up the price and quantity sold. You can use these numbers to find the price elasticity of demand for a certain type of car.
The formula you listed in the first post is just to find the change in quantity. To find price elasticity of demand, it's simply (change in quantity)/(change in price).
