The administrative authorities will need to assist them, and the whole of the industry will have to commit to educating drivers.

I guess there is always southern Africa and south and southeast Asia to draw on, but you might not like the results.

the whole of the industry will have to commit to educating drivers

There is a whole industry that will make good money to prepare and educate foreign driver in to fulfill the needs of driver need in Japan, same as foreign trainee there is a whole industry to prepare them to be in Japan. Being promised good salary in Japan is sufficient can attract clueless people third world country. Even it will cost them some amount of money that will lead them many of them into debt, even before getting any salary.

plans to accept up to 24,500 foreign nationals to work as drivers of taxis, buses and trucks in the five-year period through fiscal 2028.

After getting first driving license, need to wait another few years to be able to get class 2 driver license.

https://www.tokhimo.com/post/japan-proposes-new-visa-category-for-taxi-bus-and-truck-drivers-under-specified-skilled-worker-pro

https://jobs.guidable.co/en/articles/how-to-be-a-truck-driver-in-japan-required-licenses-and-visa