The Olinka in Alice Walker's book The Color Purple are a ficticious people. Nettie and the other missionaries travel to Monrovia, Liberia--a country on the West coast of Africa. From there, they travel by foot and canoe for four days until they come to the site of the ficticious Olinka village. Ms Walker does not tell in which direction they travelled.
There is no indication that Ms Walker based the Olinka on any particular African tribe. She herself states that she was influenced greatly by the oral tradition of her own family*. It is likely that at least some of the characteristics, customs and traditions of the Olinka are based on an amalgamation of these stories.
Instead of expending effort on what will most likely prove to be a wild-goose chase, the reader should instead seek to understand the underlying message behind the Olinka by asking him or herself such questions as:
How were the Olinka similar to Americans, either white or black of the early- to mid-twentieth century?
How were they dissimilar?
Were any of the Olinka's actions or beliefs similar to any specific characters from Nettie's past or present?
How did either the Olinka's beliefs or actions effect Nettie or Celie's children? What actions or changes did these effects have on any of them?