Try calling a few dealerships to see if they have a TRAC vehicle you
can rent.
http://www.toyota.com/html/shop/trac/index.html

You might also find a basic model at some Enterprise locations in their
"Premium" category.

I don't know if http://www.evrental.com/ has the 2004 model year or
just has the classic Prius available...

I rented one from budget in San Diego and  and once from evrental
in Phoenix.  Hertz now has some in their fleet too.

The biggest problem is that you rent a class of car, not a model+year.
Budget told me I'd have an "alternative fuel" vehicle.  I had to call
the reental site the day before flying  and talk to the manager to
ensure that they would hold a Prius for me.  I called again the day of
the flight and talked to the manager on duty who had missed the memo.
He did find me a Prius.

NOTE: Budget rent-a-car regards reservations as "requests" and not as
contracted services.  They have no qualms about taking reservations for
more cars than they own.  Their justification is that there are so many
cancelations.  I've seen them take reservations when their rental lot
was empty and the lobby full of frustrated customers.

Daniel