I think the current list in the wiki is complete. You can find it at:
I guess you might have to find the KM source code and see how each Command ID is created in C++.
Command ID's can be called by menus or by the macro language, but I don't think that is what you need for a plugin.
I hope this helps. It is quickly getting above my pay grade.
@Herr Rossi, have You checked whether the functions that don't have command IDs are from macro commands?
Perhaps the source code of macros.dll helps: It makes that macrolanguage can call the other kplugins using "plugin(pluginname)". So the key must be in macros source (although personally I don't have the slightest clue about source codes )
Just curious: What kind of plugin do you want to build, to add which functions??