There were some other whisky distilleries without Suntory and Nikka before WW2 although no more exist today.

 Most famous one was Tommy whisky and Fujisawa distillery made by Tokyo Jozo which started whisky distillation before Nikka and they competed with Suntory and Nikka as 3rd main player in 1940s and elary 1950s. But they lost competition and went bankrupt in 1955.

Japanese whisky distillery before WW2
Fujisawa distillery of Tokyo Jozo making Tommy whisky

1924-1955 Tokyo Jozo
1934?-1955 Fujisawa  distillery

 Tokyo Jozo was founded in 1924 and producing  several liquors like brandy, fruity liquor and imitation whisky made from alcohol, sugar, caramel color and other additive. They started whisky distillation in Fujisawa distillery a few years before 1937 and released "Tommy whisky" in 1937. Indeed, it is 3 years earlier than 1st whisky of Nikka. They were strong competitor of Kotobukiya (Suntory today) and Nikka in 1940s and early 1950s.
  However they lost competition in the end and went bankruptin 1955. Fujisawa distillery was sold to Kotobukiya in 1955 and then sold to Morinaga jozo (Fukutokucho Shurui today) but permanently closed in 1960s.

Taisho Seishu (Pic is Taisho seishu Taiwan HQ)

1915-1929 Taisho Seishu

(1929-1963 Takara Shuzo)

1920-1945 Distillation

 Taisho Seishu was established by Japanese in Taiwan in 1915 or 1916. It opedned Tokyo plant in 1920 and started whisky distillation with "Ideal whisky" brand but Taisho Seishu got serious damage by the Great Kanto earthquake in 1923 and merged by Takara Shuzo in 1929.
Tokyo plant became Tokyo Oji palnt of Takara Shuzo but fcility was burned down by US bombing in 1945. Takara shuzo restarted whisky distillation in 1947 but it was owned by Shirakwa distillery in Takara Shuzo  although Tokyo Oji plant continued till 1964.

Aksahikawa distillery tower of Kamiya shuzo

1880 Kamiya Shuzo

(1903 Godo Shusei)

1970s? Asahikawa Distillery

 Godo Shusei seems to have been producing alcohol for imitation whiskey since 1938. Godo Shusei was distilling also malt whisky around 1980. Although there is no certain information on which their plant was distilling malt whisky, there are 3 possibilities (Asahikawa, Kofu/ or Tokyo-Matsudo)

Lucky whisky label by Kodama jozo

1879 Kodama Jozo

1942-1950s? Distillation

 Kodama Jozo started malt whisky distillation in 1942 but they focused on sake and terminate whisky business after WW2.