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I am not an expert in this field though my government certification of management consultant indicates that I am supposed to be one.
There must always be government certified experts in any areas of subsidization. In your case, you can go ask any of Sharoushi’s, (certified social insurance labor consultants). They must have sufficient information for you. And if you further want to research subsidization in other fields of management, then Gyoseishoshi’s (administrative scriveners) are the ones that you should consult.
Actually the Ministry of Health, Labour and Welfare has a web-page explaining this kind of subsidizations. And the ministry even has a specific organization for this kind of matters, which is ” Japan Organization for Employment of the Elderly, Persons with Disabilities and Job Seekers.” It abbreviates its long name as JEED. The website written in the Japanese language does mention about the subsidization, however, the English one does not seem to be mentioning about it.