You can purchase Parallels RAS licenses online or you can contact a Parallels partner.
Visit http://www.parallels.com/products/ras/buy/
To find a Parallels partner near you, visit http://www.parallels.com/partners/locator/
Once you purchase licenses, the Parallels partner will provide you with a single license key which you can use to activate Parallels RAS. You only need one key to register and activate all your licenses.
If you don't already have a Parallels account, you will also receive an invitation to join one.
Important: A license key can be used to activate a single installation of Parallels RAS. You can change the activated installation up to three times (for backup purposes, if a previously activated server has been damaged or stolen, etc.). If you need to activate several Parallels RAS installations to work simultaneously, you need multiple license keys.