961,
Many years ago the local road assist organisation here (RACV) did a test on gauges and found one brand to be the most accurate.
Try the AA or equivalent there or online consumer reports and see what you can find.
Google gave these to me in a few seconds:
Tire Gauges quality, Halsun tire gauge | Child Car Seats
and
BRAND & MODEL PRICE OVERALL SCORE
1. Accutire MS-4000 $30.00 Excellent
2. Accutire MS-4020B $15.00 Excellent
3. Monkey Grip M8867 $10.00 Excellent
4. NAPA 90-389 $ 8.50 Excellent
5. Monkey Grip M8862 $ 3.00 Very Good
6. Pressure Inc. DT-105 $11.00 Very Good
7. AccuGauge H100X $19.00 Fair
8. Monkey Grip M8854 $ 9.00 Fair
By the way I see nothing wrong with a gauge reading consistently one way or the other. If it IS 6 lbs under is not a problem so long as it is constant you can adjust for it.
It is when it is 6 at one pressure then 3 at another then 5 at some other you can't trust the thing. Give it someone you don't like.
Peter.