You can try Power BI Pro for 60 days from within the service. The easiest way to get this is to interact with a Pro feature. For example, you can go to Get Data > Databases > Analysis Services > Connect. This will prompt you to try Power BI Pro for 60 days and allow you to use all of the Pro features.
This is tracked within Power BI itself for an individual and will not show as a license within Office 365. This is not something you can give in bulk to users of an organization.