Who hires commercial interior designers?  Is it the architect,
developer, project manager, or all of the above?  What is the best way
to go about marketing your services if you are an interior designer in
the commercial arena?  Where can I find out about jobs for commercial
interior designers in the Northeast U.S. (NY, New Jersey and New
England?)

You are likely to do better if you repost this as three separate
questions (Who hires designers? How to market your services? Where to
find jobs?)

I also suggest increasing the price. Few Researchers will spend more
than five or ten minutes on a $2 question (which, when answered,
provides the Researcher with only $1.50).