Which is why this is an AI/game balance-type issue rather than a game-mechanics issue. It's unlikely, not impossible.
FOARP, I've always respected you because you generally get China right....
Here is a list of everything wrong with Japanese intervention in Spain.
1. Europeans and the Spanish would never allow it.
Division level intervention by Japan in the European theater would not be tolerated. The Nationalists in Spain were somewhat fascist but mostly Catholic. A mostly Catholic uprising has no problem with two batallions of German Christians or 4 divisions of Italian Catholics is fine. 4 divisions of Japanese buddhists/shintoists fighting on behalf of a Catholic conservative movement would not work. The Republicans got in enough trouble by being labelled as stooges of the Soviets. Japan It would risk discrediting the Nationalist credentials.
2. Fighting effectiveness would be a lot lower than a "Japanese division"
Outside supplies were important in SCW because both sides were scraping the bottom of the barrel when it came to guns, ammunition, uniforms etc. They could not supply themselves adequately much less large foreign formations.
3. Supply would be impossible.
In the case of the other European countries, they all had a reason to be sending ships to Spain. They'd always traded with Spain. They weren't circumventing the blockade, they were sending food and clothing and clocks... whatever goods they traded before.
Japan did not have a massive amount of bilateral trade with Spain in 1935. Certainly not enough to camouflage large arms shipments.
That even goes to the idea that they could send large arms shipments, which they couldn't. Japan cannot sail past Singapore, Suez, and Gibraltar to help Spain.
From the DD we know that it takes 2 weeks to deploy into or out of a civil war. Wow... You can sail 80,000 troops around the world in 2 weeks. Realism right there.
Japan has no experience in 1936 of running a vast overseas empire or su