Google could be a good place to start searching for the information (s). Just be careful about the authenticity of the data that pick for your business plan. One way to ensure authenticity is to pick data published by established brands.

However, given my experience working with plethora startups around business planning, I am curious to understand following:

1. Why do you need info on Mobile App revenue?

If you're trying to hinge your Apps' ability to monetize on generic industry numbers then you're on a shortest possible path to getting your business plan scrapped.

Alternately, in case you aren't clear about your financial numbers then it isn't a good practice to reverse engineer your numbers by looking at revenue figures of other applications.

Thirdly, if you're counting info on mobile app revenues as a data to be mentioned under market research/analysis section then again it could be a bad idea. The data should provide an insight around your application concept and business idea.

Do feel free to reach out to me for any further help that you may need. I am just a call away to be able to provide further clarity. Thank You!!