Hi:
Enter the product number for your PC in the applicable box at the link below and you will be directed to the support and driver page for your PC.
http://h10025.www1.hp.com/ewfrf/wc/siteHome?lc=en&dlc=en&cc=us
Select the driver tab and select the version of Windows that was originally installed on your PC (32 or 64 bit).
Then there should be a link on the driver page labeled Order Recovery Media. Click on that to order online.