This font is "Caotanzhai Mao Zedong Font". This font is handwritten, and there is no exact place to download it. But this is also Mao Zedong's inscription, so just download "Caotanzhai Mao Zedong Font (or Mao Zedong Font)".
1956, Mao Zedong issued the call of "greening the motherland" and "realizing gardening", namely "12 greening movement".