If you set "developer 1", you can see the path in the console.
FindFile: Can't find menus/default/play.txt.
FindFile: ./pball/menus/play.txt
FindFile: Can't find menus/default/play_header_include.txt.
FindFile: ./pball/menus/play_header_include.txt
FindFile: Can't find menus/default/back_include.txt.
FindFile: ./pball/menus/back_include.txt
The menu path is in build38: ../pball/menus/*cl_menu*/
build39 adds the language: ../pball/menus/*cl_menu*/*cl_language*/
The setting cl_menu is "default" until you change it, so it searches in that folder like you can see at the first line of the code above. Normally that folder and the menu file in it doesn't exist, so it falls back to the normal menu folder.
So for your menu, you can add a new folder "bono" with all of your menu files and change the cl_menu setting to "bono". It should show your menu after a menu_refresh, menu_reload or game restart.