Questions regarding hacking a Yamaha BC2 magnet

[Tom May]

I think my newly acquired BC2 breath controller has a weak magnet.
Anybody know a decent source for a 3/16" x 1/16" disc magnet (not sure
of the material, but it's not a very strong magnet), or how to
remagnetize such a magnet?  I'm guessing this BC2 is from the DX7 era
and so could have lost some magnetism over time.

The reason I think it's weak is that I've got to turn the gain all the
way up to get a reasonable response curve.  It uses a magnet and a
hall effect sensor as a transducer, and I could just boost the gain on
the amplifier, but if it really is a magnet problem, I'd rather fix
the magnet.

fTom.