The 1957 Proof Lincoln cent is really difficult to find with Deep Cameo surfaces. There are probably no more than 35 - 40 examples that exist displaying full Deep Cameo surfaces. With cameo surfaces the 1957 is also somewhat difficult as there are approximately 400 - 450 examples that display full cameo surfaces.
All Proof Lincoln cents from 1950 - 1958 seem to be very difficult to find with Cameo and Deep Cameo surfaces. The 1957 seems to be in the middle, as it is not the scarcest nor the most common.