C & H Sales (which used to be C & H Surplus) in Pasadena, CA, often
has them for sale:

C & H Sales
tel: 800-325-9465.
candhsales@earthlink.net
http://www.candhsales.com

For the record, a simple home-made water gauge is much more accurate
than any consumer-quality dial gauge.

Regards,
Bob Loesch, in beautiful Lake County, California, USA
http://www.jps.net/rrloesch