What is the average in revenue sales for amateur porn sites on the
web? What types are the highest grossing amateur porn on the web?

The reasonable answer would be dependent upon a fair amount of
participants to publisher their sales to determine an 'average'.  I
can't think of a good reason why 'any' company would want to
voluntarily do that, much less get a lot of companies to.

The only time a company is 'required' to publish their financial
results is if they are a public company.  Can't think of a single
public company that publishes amateur porn.

Don't wish to discourage you, but I doubt if you'll get an answer.