https://forums.adobe.com/thread/2550667

Search in masterpages

    if ( app.documents.length > 0 ) {   
        if ( app.scriptPreferences.version >= 6 ) {  
            app.doScript( main, ScriptLanguage.JAVASCRIPT , [], UndoModes.ENTIRE_SCRIPT, "Search in masterpages" );           
        }   
        else {  
            main();  
        }  
    } else {  
        alert ( "No documents open!" );  
    }  
      
    function main() {  
      
        // Your settings  
        // ---  
        var searchList = [  
            [ "USA" , "Obama" ],  
            [ "rocket" , "sky" ],  
            [ "New York" , "Los Angeles" ]  
        ];  
      
        app.findGrepPreferences = app.changeGrepPreferences = null;  
        app.findChangeGrepOptions.includeMasterPages = true;  
        var target = app.documents.everyItem().masterSpreads.everyItem().textFrames.everyItem();  
          
        for ( var j = 0; j < searchList.length; j++ ) {  
            var curSearch = searchList[j];  
            app.findGrepPreferences.findWhat = curSearch[0];    
            app.changeGrepPreferences.changeTo= curSearch[1];    
            target.changeGrep();    
        }       
        app.findGrepPreferences = app.changeGrepPreferences = null;   
    } // main