How could I add this?

How could I add something like NulledBB has here - http://nulledbb.com/statistics/ (the monthly stats thingy)

But make it for the amount of traffic that has visited.

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Anyone help with this please?

I think this is mostly custom. But most of it is from MyBB it self I believe.

You'd have to ask AmN or ask a developer to make one for you.