There are three different ways for menus/toolbars to be instantiated:
the old way, using macros. Before A95, this was the only way, so a lot of older apps (i.e., those converted from earlier versions) may still use macros for the menus.
defining them by hand, using the CUSTOMIZE function that you get when you right click on a toolbar in Access.
in code, using the Application.Commandbar object.
For the first you can browse your macros and see if any of them are menu macros.
For the last, you can do a search in the code for CommandBar.
For the second, just look at them through the built-in menu customization tools. Keep in mind that you may have to check them off to get them to be visible, and that the list is in no rational order. Likewise, some menus/toolbars are hidden from the customization interface. Also, you might need to look at the CUSTOM toolbar menu item.