Install 3rd party app into a Scratch Org using sfdx

Question

I'm having a hard time figuring out how to include a 3rd party managed package into a Scratch Org as part of a project deployment.

The 3rd party app is CalendarAnything

Reading through this and this it seems that I would need to include the dependency definition in my sfdx-project.json

"dependencies": [ 
      {
        "package": "OtherOrgPackage@1.2.0"
      }
  ]

How would I work out the package name and version from the AppExchange listing and how does this work with paid apps anyway?