Droog, I believe the only way to get a Davida helmet here in the states is via British Classics at
http://www.british-classics.com
I believe they only sell direct
There are tech differences between DOT and Euro certification, but both are similar. The basic problem for us bikers is that a helmet legal in the US must be DOT certified. If it just has the Euro cert., it's not legal over here. One of the Davida styles (the Classic Jet, I think) is DOT cert., but it's the only one.
Hope this helps.