Patent search firms are business that perform database and library
research for patent-related cases.  There are many different types of
searches typically offered by search firms.  A good overview can be
found at http://www.gilmanresearch.com/pages/944486/index.htm

I would like to know:

(a) The total number of patent search firms.  I would like this
information to be from a reputable source, not a guess by counting the
number of links from Yahoo or Google Directory.  The number of firms
in the US would be fine... a breakdown by country would be worthy of a
tip.

(b) Some indication of the yearly revenue for some of the large US search firms.  

Thank you,
Chess