Something i have thought of doing is using a good quality PC headset, such
as the one i have, senheiser pc130, and using it on the ic t90a.
I would have to built a small power pack to supply voltage to the microphone
cartridge in the headset, but as far as i can tell, the impedance match
should be very close.
I wonder what the collective opinions are regarding this kind of setup are
on the list?
I suspect the microphone cartridge wouldn't have enough output to drive the
radio's mike amp, but perhaps an extra tripple A battery or extra watch
battery in the power pack would solve that issue.
I could likely use 1.5V watch batteries, since the headset microphone
shouldn't require much current to operate for long periods of time, and it
really only requires 1.6V or so to work.  So, a pair of small batteries in
series should supply around 3V, plenty of voltage to keep the mike hot.

73
Colin, V A6BKX