Many British and American citizens, as well as other Europeans, find short-term volunteer work with international or local NGOs. Finding paid work can be more challenging, but not impossible, especially if you are trained in a field that is lacking qualified locals. Be aware that you may have to pay for an annual work permit, which costs $1000.
Sierra Leone is an excellent place to pursue independent research. Possible areas of study are African music, dance, history, politics, as well as zoology, botany, traditional medicine. Krio teachers are easy to find. Unfortunately, the idea of advertising private drum and dance lessons hasn't caught on like it has in other West African countries like Ghana and Senegal, but the possibility exists for those willing to search for a qualified instructor. It's unlikely you'd want to come to Sierra Leone to study at Fourah Bay College or Njala University. These institutions are famous for corrupt practices such awarding of grades in exchange for monetary payment or sexual favors, and the facilities are generally poor. Most Sierra Leoneans with the financial means aspire to attend university abroad.