Azure Analysis Services can be found within the Data and Analytics tab in the Azure Marketplace. Clicking the Analysis Services icon presents a configuration blade to define the new resource including its location (data center region) and pricing tier.
In the following screenshot, a new Azure AS instance (Frontline) is created in the North Central US region and for the S0 pricing tier:
The view full pricing details link has been accessed in the preceding screenshot to expose additional SKUs currently supported. As of this writing, the largest Azure AS instance is ...