I recently had the same issue and while I was able to find some samples on the forums, they were all dated and slightly different. My best suggestion is simply to download the latest version of Desktop and re-install. That way you'll get all the latest sample data sets.
Mashoor, I've attached a packaged workbook with all the sample data sources included. Any twbx file is really a zip file with a different extension name. So you can get at the data by opening the file in a Zip Utility and extracting the files in the data folder. The ones in this workbook were installed with 8.0.3 installed (I think).
Hope this helps,