Vic,  The R.A.G. company makes a plastic reiterating valve similar to
the one you are speaking about.  It would be quite simple to make one
yourself.  If you have a brass "T" nipple and can get a 1/8" brass rod,
that is all that is needed.

The top right leg of the "T" goes to the snare beater valve and the
bottom leg of the "T" goes to the tracker bar.  The 1/8" brass rod
slides into the left leg of the "T" to interrupt the air from the
tracker bar when the beater pneumatic collapses.  Care must be taken
to assure that there is no binding when the rod slides into the "T".

This "T" was made from soldering two straight nipples together then
drilling through the bottom leg and clearing out the top nipple with
a 1/8" drill.  If the rod does stick a very fine sand paper can be
used to reduce it's size so that it slides freely.

Good luck,
Tim L'Amoureux