The Belgians *did* get another colony after the Congo - They got Ruanda-Urundi. Anyway, Leopold the I (father of the infamous Leopold II) was very adamant about overseas colonization but didn't have the means to do so - He looked pretty much everywhere, from Hawaii and the South Pacific to Guatemala to Brazil to Guinea and even to Texas. That would be too early for your POD, however.
The best I could see is *maybe* the Belgians taking interest in North Borneo, the lease for which was offered to the United States, Austria-Hungary, and Italy at one point. Why not Belgium as well? Belgium might also be able to grab some islands in the South Pacific, perhaps the Solomons, which I'm pretty sure the Belgians actually looked at if I remember correctly. Again, the main problem is going to be funding.