public IEnumerable<Item> Search( 
   string searchString
)

{
  var gpItems = CoreModule.CurrentProject.Items.OfType<GeoprocessingProjectItem>();

  // go through all the available toolboxes
  foreach (var gpItem in gpItems)
  {
    var itemsInsideToolBox = gpItem.GetItems();

    // then for each toolbox list the tools inside
    foreach (var toolItem in itemsInsideToolBox)
    {
      string newTool = string.Join(";", [toolItem.Path, toolItem.Name]);
      // do something with the newTool
      // for example, add to a list to track or use them later
    }
  }
}