Many shower heads today achieve the 2.2 GPM ( some now even less) by internal design, not a simple restrictor at the inlet.
The best flow is obtained from a garden hose, but there are legal ( meaning 2.2 GPM) shower heads which work quite well. Many Delta and Alsons fall in that category. Major hotel chains are sensitive to pleasing their guests, and among some Flag Specified heads are the Kohler Forte, Symmons S2005, and the Moen Revolution. Among the hotels specifying one or more of the above are Holiday Inn, Hilton, and Marriott.
If you choose not to work within the framework of the law and the water conservation needs of your community, you are on your own.