I would check out any local aircraft instrument repair facility, many have instrument fitters who like to try something slightly different and your Sestral barometer is simple compared to many altimeters.
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence