User-Agent Switcher for Chrome - Version: 1.0.3
I have this installed and it works fine in Iron latest for windows. I will say that it was installed in an earlier version of Iron.
There is an experimental version called spoofer.crx here>>
http://spoofer-extension.appspot.com/ under the "10/8/2011 - New, experimental version available!" banner. Download link is hard not very easy to see, so look closely.
OK, I don't let them install from the web. I right click and 'Save Link As' and install it from my machine.
Having said all of that, have you given consideration to UA.ini? It is a file that you can set up, and add your own browser(s) you want spoofed, instead of somebody else's idea of what you should have. Just a thought.