Where can I obtain a valuation of a Bernd Kroeber monoprint entitled
Red City Flag purchased in the mid-70's when the artist was a resident
of California? Results of Google previous search was a list of German
art exhibitions, but no valuation figures. This is needed for
insurance purposes and possible future sale.

Try searching for a valuation on http://www.artnet.com/  It only costs
$30 for 10 searches, and might throw up a sale of a Kroeber monoprint.
You could of course simply use the figure you originally paid for your
print, allowing for inflation, plus a bit for a genuine increase in
value. The fact that Kroeber is not widely available on the Internet
seems to indicate that his work is not very highly sought or valued -
though personally I like the monoprints shown on 
http://www.knechthausen.stade.net/bilderausstellung.html