John Bartley's suggestion of clock suppliers paid off big time. Although his suggestion of inlineovals.com didn't work out, I found exactly what I needed, a 4 1/4" convex round dial glass at
http://www.timesavers.com for the princely sum of $4.25! They have convex glass up to 15" diam. and more, and the price seems to be about $1/inch of diameter.
Thought this info might be of use to some of you.
Tom