- Albert, King of the Belgians and Buren, Raymond. Journal de route du Prince Albert en 1909 au Congo. 2008.
- Le Congo belge en images. 1927. (Discusses Prince Leopold's visit in 1926)
- Crokaert, Jacques. Boula Matari: au Congo belge avec le Roi Albert. 1929.
There are also the Carnets de Voyages (1919-1983) of Leopold III which, presumably, include his notes on his African trips in 1926 and 1933. I hope in the future to be able to take a look at these (via interlibrary loans and such) but it will probably take a while!