There seems to be some confusion in the name. It is possible that:
* The name is misspelled: There may be a different name for the people or the region.
* The myth is not widely documented: There might be a myth but it's not widely known or documented.
* The myth is related to a different group: The myth might be associated with a related group or tribe in the area.
I recommend further research using different spellings and sources. You can try looking for:
* Different spellings of the name: Check for variations like "Humbukushu," "Hambukushu," etc.
* Related tribes: Explore myths and legends of other groups in Ngamiland, such as the Subia or Bayei.
* Local sources: Contact museums, libraries, or cultural organizations in Ngamiland or Botswana.
Please provide more context or specific information about the myth you are looking for so I can be more helpful in your search.