These buttons are deprecated and should be replaced by the corresponding ones in GTK+:
http://library.gnome.org/devel/libgnomeui/stable/GnomeDialog.html#GNOME-STOCK-BUTTON-CANCEL:CAPS
http://library.gnome.org/devel/libgnomeui/stable/GnomeDialog.html#GNOME-STOCK-BUTTON-CLOSE:CAPS
http://library.gnome.org/devel/libgnomeui/stable/GnomeDialog.html#GNOME-STOCK-BUTTON-DOWN:CAPS
http://library.gnome.org/devel/libgnomeui/stable/GnomeDialog.html#GNOME-STOCK-BUTTON-OK:CAPS
http://library.gnome.org/devel/libgnomeui/stable/GnomeDialog.html#GNOME-STOCK-BUTTON-UP:CAPS



./gnome-commander/plugins/fileroller/file-roller-plugin.c:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_OK,
./gnome-commander/plugins/cvs/interface.c:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CANCEL,
./gnome-commander/plugins/cvs/interface.c:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_OK,
./gnome-commander/plugins/cvs/interface.c:        GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CLOSE,
./gnome-commander/plugins/cvs/interface.c:        GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CLOSE,
./gnome-commander/plugins/cvs/cvs-plugin.c:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_OK,
./gnome-commander/libgcmd/gnome-cmd-string-dialog.c:        GNOME_STOCK_BUTTON_CANCEL, GTK_SIGNAL_FUNC (on_cancel), string_dialog);
./gnome-commander/libgcmd/gnome-cmd-string-dialog.c:        GNOME_STOCK_BUTTON_OK, GTK_SIGNAL_FUNC (on_ok), string_dialog);
./gnome-commander/src/plugin_manager.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CLOSE, GTK_SIGNAL_FUNC(on_close), dialog);
./gnome-commander/src/gnome-cmd-bookmark-dialog.cc:        dialog, GNOME_STOCK_BUTTON_UP, "move_up_button",
./gnome-commander/src/gnome-cmd-bookmark-dialog.cc:        dialog, GNOME_STOCK_BUTTON_DOWN, "move_down_button",
./gnome-commander/src/gnome-cmd-bookmark-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CLOSE,
./gnome-commander/src/gnome-cmd-chmod-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CANCEL,
./gnome-commander/src/gnome-cmd-chmod-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_OK,
./gnome-commander/src/gnome-cmd-dir.cc:        GNOME_STOCK_BUTTON_CANCEL,
./gnome-commander/src/gnome-cmd-patternsel-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CANCEL, GTK_SIGNAL_FUNC (on_cancel), dialog);
./gnome-commander/src/gnome-cmd-patternsel-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_OK, GTK_SIGNAL_FUNC (on_ok), dialog);
./gnome-commander/src/gnome-cmd-chown-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CANCEL,
./gnome-commander/src/gnome-cmd-chown-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_OK,
./gnome-commander/src/gnome-cmd-xfer-progress-win.cc:    button = create_stock_button (w, GNOME_STOCK_BUTTON_CANCEL, GTK_SIGNAL_FUNC (on_cancel));
./gnome-commander/src/gnome-cmd-options-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dlg), GNOME_STOCK_BUTTON_CLOSE,
./gnome-commander/src/gnome-cmd-options-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CANCEL,
./gnome-commander/src/gnome-cmd-options-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_OK,
./gnome-commander/src/gnome-cmd-options-dialog.cc:    button = create_stock_button (parent, GNOME_STOCK_BUTTON_UP, GTK_SIGNAL_FUNC (on_app_move_up));
./gnome-commander/src/gnome-cmd-options-dialog.cc:    button = create_stock_button (parent, GNOME_STOCK_BUTTON_DOWN, GTK_SIGNAL_FUNC (on_app_move_down));
./gnome-commander/src/gnome-cmd-options-dialog.cc:        GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CANCEL,
./gnome-commander/src/gnome-cmd-options-dialog.cc:        GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_OK,
./gnome-commander/src/gnome-cmd-options-dialog.cc:    button = create_stock_button (parent, GNOME_STOCK_BUTTON_UP, GTK_SIGNAL_FUNC (on_device_move_up));
./gnome-commander/src/gnome-cmd-options-dialog.cc:    button = create_stock_button (parent, GNOME_STOCK_BUTTON_DOWN, GTK_SIGNAL_FUNC (on_device_move_down));
./gnome-commander/src/gnome-cmd-options-dialog.cc:    gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CLOSE,
./gnome-commander/src/gnome-cmd-prepare-xfer-dialog.cc:    dialog->cancel_button = gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_CANCEL, NULL, NULL);
./gnome-commander/src/gnome-cmd-prepare-xfer-dialog.cc:    dialog->ok_button = gnome_cmd_dialog_add_button (GNOME_CMD_DIALOG (dialog), GNOME_STOCK_BUTTON_OK, NULL, NULL);
./gnome-commander/src/gnome-cmd-file-selector.cc:        GNOME_STOCK_BUTTON_CANCEL,
./gnome-commander/src/gnome-cmd-delete-dialog.cc:    button = create_stock_button_with_data (data->progwin, GNOME_STOCK_BUTTON_CANCEL, GTK_SIGNAL_FUNC (on_cancel), data);


For your interest, remaining GNOME_STOCK_* items that have NOT yet a GTK+ replacement are:
./gnome-commander/src/gnome-cmd-main-win.cc:        GNOMEUIINFO_ITEM_STOCK(NULL, _("Send files"), file_sendto, GNOME_STOCK_MAIL_SND),
./gnome-commander/src/gnome-cmd-main-menu.cc:            GNOME_APP_PIXMAP_STOCK, GNOME_STOCK_TRASH,
./gnome-commander/src/gnome-cmd-main-menu.cc:            GNOME_APP_PIXMAP_STOCK, GNOME_STOCK_ABOUT,
./gnome-commander/src/gnome-cmd-file-popmenu.cc:        GNOMEUIINFO_ITEM_STOCK(N_("_Delete"), NULL, on_delete, GNOME_STOCK_TRASH),
./gnome-commander/src/gnome-cmd-about-plugin.cc:    image = gtk_image_new_from_stock (GNOME_STOCK_ABOUT, GTK_ICON_SIZE_BUTTON);
./gnome-commander/src/gnome-cmd-file-popmenu.cc:        GNOMEUIINFO_ITEM_STOCK(N_("Send files"), NULL, file_sendto, GNOME_STOCK_MAIL_SND),