As a fellow hoarder of odd things thready, I checked my out of date tap
and die list and found taps but no dies of the correct size. However I
recently pick up a stash of such things and in a proper Galootish time
frame have dug through and found a single 8-40 die. If you haven't given
up and made one already I would be happy to put some threads on a bit of
steel rod and send it your way. Then all you would have to do is fit the
Keeper of the only 1 1/2 - 56 tap and die set known.