Note there is no instructions which instruct you how to request one of these. You should phone Dell Technical Support for your region to request one. Alternatively post in the Microsoft OS Forum and hopefully a Dell member will be able to assist you with the procurement of one.
Note it is likely that these will not allow for clean installation and you will have the preinstalled software bundled.
If you are unable to procure recovery media see Windows Reinstallation Guide/A Clean install of Windows 7.