Autodesk has been officially discontinued and is no longer available for direct purchase or official download from Autodesk. However, you can still access original documentation and explore modern alternatives. Official Documentation (Solid Papers)
The short answer is: Autodesk officially discontinued AutoSketch on October 26, 2016. It is no longer available for purchase or direct download from the Autodesk website . If you are looking for a copy today: autosketch 10 top download
(Cross-platform)