His work—during his lifetime—was exhibited worldwide and currently is found in many prominent museums featuring modern art (I use the small “m” here deliberately).
Find out more about the artist at www.HansHofmann.org.
These pieces were shown at Expo Chicago 2012 by Ameringer, McEnery Yohe (NYC). They have a number of pieces by the artist. I would suggest their site has some of the more striking pieces.