Where can I find information on sales figure of Apple products?
Apple discloses many of these informations with their quarterly reports. You'll find many sources discussing and analysing these by having a quick search in Google, but you'll also find the original announcements on Apple's website.

Have a look at http://investor.apple.com/

A listing of all press releases with quarterly reports can be found on this page: http://investor.apple.com/results.cfm