Hi Lallo!
If you want a word for ‘the migration of a people from their ancestral homeland’, you could try something related to tunkan (cf. tunga/tungan in the AKT dictionary; and episode 7 of Na baro kè about the word/concept), which refers to both ‘foreign land(s)’ and ‘adventure’.
This word is at the root of expressions like tungaranke (which is often translated as ‘emigrant’, ‘migrant’ or sometimes ‘adventurer’ [cf. the dual meaning of tungan]).
As I said, in my experience, there isn’t currently a conventional one-to-one translation that lines up with “diaspora” in the sense that you describe. But you could potentially say something like:
tunkarankelu
ߕߎ߲ߞߊߙߊ߲ߒߞߋ ߟߎ߬Lit. ‘migrants’ / ‘aventurers (seeking fortune away from home or abroad)’
Or:
tunkannamɔɔlu
ߕߎ߲ߞߊ߲ߠߊߡߐ߮ ߟߎ߬Lit. ‘people in/on tunkan’
The tricky thing is that the term is often used for people who have themselves actually left their homeland and are abroad. I’m not sure that out of context someone would interpret it in Maninka (or Manding, in general) as referring to people who ancestrally are connected to a place, but did not grow up there and live (e.g., in the way we say, “the Guinean diaspora”, “the African diaspora”, etc., with it referring to people who might be one or multiple generations removed from Guinea or Africa, have never been there, etc).
But meanings are always growing, shifting or being stretched! Hope that helps 
PS - I checked Kantè’s French-N’ko dictionary, Jaanɛ’s French-N’ko dictionary, Bailleul’s French-Bambara dictionary and some older lexicons and none of them included an entry for “diaspora”.