What percent of revenue is spent on marketing plus sales activities at
accounting firms vs consulting firms vs other industries and
businesses?

I would love to find a single source that gives a definitive answer
across many industries, but I suspect this does not exist.  I do
expect that you can find surveys done in the last few years for
individual professions and for industry segments.  I have seen some
recent figures for law firms (published by Law Firm Inc and by the
Legal Marketing Assoiciation), and would like to compare them to other
professions and businesses.