There are a lot of Japanese and their descendants living in other countries. Maybe they could offer some incentives to entice them back. Peru has a lot of Japanese, and of course America does. The recently arrived Japanese people I know like America because here there is more living space and they can afford more kids (usually 3) than they would have had in Japan. If Japan made housing for large families affordable and available, maybe more would return.
Second or third generation Japanese are not generally accepted by the mainland Japanese.
Japanese Brazilians and Peruvians would be a source of potential immigrants.