I would be very surprised if you could not find Tamarind in Nigeria,
as Tamarind is indigenous to tropical regions of Africa including Nigeria, Sudan and Cameroon. It’s also not only growing in tropical but also in subtropical countries around the world. Because Tamarind is non-perishable items, it could be easily imported from other countries with low cost.
Tamarind is very popular among Asian and Caribbean (to some extends) cuisines. So unless there is no sizeable number of Thais, Indians, Malays, Filipinos, Indonesians, you will definitely find Tamarind easily in any Asian Supermarkets across continents. The price of tamarind is certainly more expensive compared to Indonesia, as it will need to be imported from tropical, sub-tropical countries.