How can I find the SourceLocation of a character after a SourceLocation in a Clang AST?

I'm trying to use the Clang Lexer library to find the location of a token (specifically the left brace of a namespace declaration). My idea (since the NamespaceDecl doesn't have a method for it) was to find the location of the first left brace after the start of the namespace declaration. However, looking at the Lexer API, I can't seem to find a short and simple way to do this while visiting an AST. Any suggestions/alternatives without having to do something drastic like reparse the code?