If you need a tourist visa, you can get it upon arrival. Sierra Leone is in GROUP 2 - citizens who need a visa but do not have to get it prior to arrival.
However, if you plan to move to Bolivia to request residency and live and work here, you have to arrive on a SPECIFIC PURPOSE VISA (visa de objeto determinado) and that has to be acquired from a Bolivian consulate in your country, or any nearby country, prior to arrival - this pertains to anyone from any country.