Sources
In addition to online auctions and coin/currency dealer websites, African banknotes can be found at estate auctions, flea markets, and may also be available from investor resources like Forex, ING, and Scottrade.
Counterfeiting
Be sure you're dealing with a reliable source when buying African banknotes. Counterfeiting of both goods and currency is a major problem in many African countries. In August 2008, Mozambique President Guebuza stated that such counterfeiting was a serious threat to the entire Mozambican economy.
Fun Facts
A popular method for collecting African currency is by "Heads of State." Currency portraying political figures who have had a surprisingly long reign are highly collectible, as is currency featuring rulers who had a very short time in power.