"toolbar.get.config.xml" is a configuration file associated with the "toolbar.get.desc.xml" WebScript. It is true that this association is handled by the WebScript framework (which can be considered part of the Surf framework) but it should not be confused with the ConfigService part of Surf that processes standard configuration files.
If you really want to know the bit of code that handles it then you should look at the "setupScriptConfig()" method in the org.springframework.extensions.webscripts.AbstractWebScript class.
…but all you really need to know is that a WebScript will look for a configuration file that has the same prefix up to the HTTP method (in this case "toolbar"). WebScript specific configuration needs to be processed by the WebScript controller. For the "toolbar.get.js" file this is actually handled by the imported "toolbar.lib.js" file.
