Hello! First of all i have to apologize for my bad English.

I'm an Brazilian Historian, but for coincidence, i'm specialized in Japanese Immigration to Brazil.

I looked in my principal bibliography and do not remember any mentions about it, and also do not remember any sources about this specific question. Despite that, we can suppose katanas were probably pretty uncommon among Japanese-Brazilian at that times. In fact, any weapon was.

I suppose that because the idea that Japan do not lose the war became widespread among Japanese immigrants and their descendants for the complicated situation of that community during WWII.

Dictator Getúlio Vargas adopted an large number of repressive and racist measures against Japanese, as occurred in the US, after Brazil get in WWII in 1942. Japanese-born people was prohibit of organize public meetings, maintain ethnic schools, speak their language at streets, have any radio equipment, carry or possess fire guns or travel without an government authorization.

At that time, the large part of Japanese-Brazilian live in rural colonies producing coffee and other agricultural products. So they became basically isolated at that grounds. Some of people who live at coast were expelled by the government, who considered peoples who live in this places for decades potencial infiltrate spies who can help Japanese Marine in an possible attack. In many cases, this people (also who occurred in US) was send to something similar to an concentration camp. In São Paulo city, where did exist an expressive Japanese community at war time, neighborhoods and streets with an considerable number of that immigrants was largely policed. In fact, the period between 1938-1950 registered several Japanese immigrants imprisonment.

This explain why some researches made in the 1950's at Japanese Immigration cores point the most part of Japanese Brazilian do not believe in Japan loss. They are unable to have any official news because most part of radios are confiscated, they were isolated from the cities, ethnic press was also prohibited and they are in trouble against Brazilian State and their came from an country who claimed to have an unbeatable army. Also, accept Japan loss are like to accept they can not back to their country. So, a small number of that people actually integrated Shindo Renmei, but most part of them can be considered supporters. The ones who accepted the loss were normally families that progressed socially and have the appropriate access to World News.

So, backing to your question, if anyone has any weapon, this had to be hidden. Certainly, most of that weapon was manufactured by the immigrants with native available resources, although some of then may came from Japan with the Immigrants . Not all the killings attributed to Shindo Renmei were performed with Katanas, in fact the minor part of then was. This is more an kind of symbol. Documentary "Yami no ichinichi, o crime que abalou a colônia" (available in youtube) interviews integrants of Shindo Renmei who killed another immigrant who accepted the loss whit fire gun shots.

Sources

CYNTROWICZ, Roney. Guerra sem guerra – a mobilização e o cotidiano em São Paulo durante a Segunda Guerra Mundial. São Paulo: Geração Editorial, 2002.

HANDA, Tomoo. O imigrante japonês: História de sua vida no Brasil. São Paulo: T.A. Queiroz, 1987.

LESSER, Jeffrey. A negociação da identidade nacional: imigrantes, minorias e a luta pela etnicidade no Brasil. São Paulo: Editora Unesp, 1999.

SHIZUNO, Elena Camargo. Os Imigrantes japoneses na Segunda Guerra Mundial: Bandeirantes do oriente ou perigo amarelo. Londrina: Eduel, 2010.