CellPrint@Cell[BoxData["MyTag"], "Input", CellTags -> "MyTag"]
Print[Button["Print Button",
   CellPrint@Cell[BoxData[
      ToBoxes@Button["Cases[\"MyTag\"] Cells",
        Print@
          Cases[NotebookGet[EvaluationNotebook[]],
           Cell[___, CellTags -> "MyTag", ___], Infinity];
        ]
      ], "Input", CellTags -> "MyTag"]
   ]
  ];