I am trying to gauge the size of the landloard and property management
market in the United States and abroad.

A landlord would be considered as an individual that has a second home
or investment property that they rent. Keep in mind that a landlord
isn't necessarly an individual with just a couple single family homes.
It can also be a individual that owns several commercial properties
that are for rent. An example of this would be a developer that buys
vacant land and builds to own and manage.

A property management company would be a organization that provides a
service to various property investos/owners to manage their
properties. They typically charge a monthly fee and handle everything
from rent colletion to maintenance on the property.

There are some sources that I have identified for gathering this
information such as:
1. US Census Data
2. Acxiom

But, I need more sources of this information. I am guessing there must
by news and other media publication which have thrown a number out
before.

The answer must be submitted with a source of the figure and a link to research.

Land lords are finding renting and leasing not very profitable in much
of the USA, because of decreasing ethics, especially among lawyers =
dispicable. The number of management companies has likely doubled in
the last ten years. Commercial buildings for lease have also
increased, but not housing to be rented to individuals and family as
living quarters. Much of what a magazine would like to tell land lords
is not politically correct.  Neil