For Alfresco Enterprise edition you need to get into contact with the (regional) Alfresco sales team. If you can't find someone to contact directly via general networking (e.g. LinkedIn), you may want to try the general contact forms on the Alfresco web page.
Note though: There is no such thing as a single-user license for Alfresco Enterprise. Typically, an Enterprise license starts with user counts in the low hundreds. The experience of most in the Alfresco community is that the (very few) extra features that Alfresco Enterprise brings (without considering its extra addon modules) are often not really relevant for small installations and Alfresco Community Edition can serve such use cases just as well.
