The .320 Garrucha (Derringer) cartridge has been made for some time in Brazil. I don’t have exact dates, but the last CBC Catalog I have that mentions it, while undated, has a passage in the Introduction that refers to exportations “exported up to 1979,” so the catalog is no earlier than that year. I will try later to have my friend post pictures of the .320 and .380 Garrucha rounds, from the catalog.
Regarding Rossi-headstamped rounds, an answer in the Questions and Answers column of the “American Rifleman” magazine, issue of November 1980, pages 60 and 61, claims that the .320 Garrucha casrtridge “is specifically made for this gun by Rossi, and used a 99-1 lead-antimony bullet, a small charge of black-powder, and a Berdan primer.” A photo caption of a picture showing some cartridges scattered around a Rossi box says the the .320 is the only cartridge made by the Rossi factory. The article also shows what is purported to be a Rossi factory drawing of the cartridge. I have heard in the past from good Brazilian sources that CBC made the cartridges for Rossi, so this information from the NRA must be accepted with reservations, unless someone has precise information that confirms or repudiates it.