Curt,
Not sure when they started, but the earliest 2" gun in my collection dates to January of 1935.

As for the 3" guns, the earliest I've found is a pre-model numbered post-war gun that dates to July of 1959. I've not heard of any 3" guns that were made pre-war except for maybe the custom one-off guns that were shipped to Ed McGivern. Mike Priwer can possibly give you some perspective on those.