You mean Aspose.Cells.Pivot nampespace? Yes, this namespace are included in the later/new versions and all the pivot tables related classes with their members are moved to that namespace.
For your older version e.g v4.8.1.x that you are using, all the relevant pivot tables are in the main Aspose.Cells namespace. So, you should or can only import Aspose.Cells namespace for your project/application. All your provided list of classes are there in the main Aspose.Cells namespace.
Using older version, your code might look like this:
//Adding a PivotTable to the worksheet
int index = worksheet.PivotTables.Add("=Data!A1:F30", “B3”, “PivotTable1”);
//Accessing the instance of the newly added PivotTable
Aspose.Cells.PivotTable pivotTable = worksheet.PivotTables[index];