code: public function getFileUpdatesWithHandle($handle, $storeId, $area)
      {
          /** @var array $updateFiles */
          $updateFiles = Mage::helper('sheep_debug')->getLayoutUpdatesFiles($storeId, $area);
  
          /* @var $designPackage Mage_Core_Model_Design_Package */
          $designPackage = Mage::getModel('core/design_package');
          $designPackage->setStore($storeId);
          $designPackage->setArea($area);
          $designPackageName = $designPackage->getPackageName();
          $layoutTheme = $designPackage->getTheme('layout');
  
          // search handle in all layout files registered for this area, package name and theme
          $handleFiles = array();
          foreach ($updateFiles as $file) {
              $filename = $designPackage->getLayoutFilename($file, array(
                  '_area'    => $area,
                  '_package' => $designPackageName,
                  '_theme'   => $layoutTheme
              ));
  
              if (!is_readable($filename)) {
                  continue;
              }
  
              /** @var SimpleXMLElement $fileXml */
              $fileXml = $this->loadXmlFile($filename);
              if ($fileXml === false) {
                  continue;
              }
  
              $relativeFilename = str_replace($this->getBaseDir(), '', $filename);
  
              /** @var SimpleXMLElement[] $result */
              $results = $fileXml->xpath("/layout/{$handle}");
              if ($results) {
                  $handleFiles[$relativeFilename] = array();
                  /** @var SimpleXMLElement $result */
                  foreach ($results as $result) {
                      $handleFiles[$relativeFilename][] = $result->asXML();
                  }
              }
          }
  
          return $handleFiles;
      }
docs: Returns layout files that have updates for specified handle
  
  @param string $handle
  @param int    $storeId
  @param string $area
  @return array