Although my knowledge of Band Organs is very limited, there are a
couple comments I'd like to make.  Theater organ pipes *are* HIGH
pressure pipes - typically at 10-15 inches of wind.

Voicing: I doubt theater organ pipes can be said to either be voiced
better or voiced worse than church organ pipes.  It all depends on the
maker of the pipes, the maker of the instrument, and how they were
voiced for the particular house.  They are also voiced "differently".

There may be some other problems, though, with using theater organ
pipes for such a project.  For instance, I believe band organ string
pipes are wood, whereas theater organ string pipes are metal.  Perhaps
with the right pressure and proper voicing, something could be altered.
(?)

> You won't find anything in the "Theatre Organ Pipe Warehouse" you
> mention.  (By the way, I do not know of a warehouse full of theatre
> organ pipes, do you?).

Century Pipe Organ Co. in Minneapolis MN.  (I have no affiliation with
them, although I've purchased many organ parts from them.)

If cost is not an object, there are companies that will make pipes
(e.g.  Organ Supply Industries in Erie PA). Last time I checked,
a rank ran between $1200 and $2000.