Even good US and UK bike shops seem to omit chainguards.
They are standard equipment on Dutch city bikes:

http://www.gazelle.nl/cgi-bin/bikes/...egment=comfort

A Giant dealer (they are 1/2 Dutch) may be able to source one, since their Dutch models often come with chainguards.

Give Harris Cyclery a go as well:
http://www.sheldonbrown.com/harris/index.html

They dont work well with front mechs, but if you live in a flatter area, and want a clean utility bike, rather than a racer, then fit a single chainring. A wide range cogset at the back will cover all the range you need. You could even go really continental and fit a Sachs or Shimano 7 speed hub gear.