I've been reading with interest the brass reeds for trumpets posts.
You might be able to contact an organ supply house like Organ Supply in
Erie, Pa., telling them the length of the pipe (8', 4'?), and the note
name, the size of the shallot (maybe), and the wind pressure (8"?).
They may be able to supply the right reed brass for the trumpets being
made.

I got my brass in small sheets.  We used to cut our reeds in the organ
shop I was employed in by cutting them with a "scorer."  It was a
three-cornered tool almost like a soundboard shimming tool.  You mark
out the width of the reed from the shallot width.  Usually they are the
exact width and length of the flat area on the shallot.  The reed brass
is then scored over and over again until the reed separates from the
rest of the sheet of brass.

Voicing reeds is best done by a professional, using a curved wood block
on which the reed is laid.  A round rod is smoothed over the surface of
the reed in one direction until it takes the curve needed for the reed
to vibrate.  The reed can be rubbed from the end the reed or in the
middle at a certain point.  By changing the point at which the rubbing
starts, the voicing can be different.  I'm sure people have done it
themselves, but if it were me and I put all that work into building an
organ, I would have the trumpets voiced by a professional reed voicer.

On the East Coast here we use a firm in Hagerstown, Maryland, called
Trivo.  There are people there that have done band organ trumpets
before, but they mostly voice church organ pipes.  I have several books
on reed pipes, and as with anything, "the more you know, the more you
know you don't know"

Tony Marsico