Version 12 of the ReportViewer bits is referred to as Microsoft Report Viewer 2015 Runtime and can downloaded for installation from the following link:
https://www.microsoft.com/en-us/download/details.aspx?id=45496
UPDATE:
The ReportViewer bits are also available as a NUGET package: https://www.nuget.org/packages/Microsoft.ReportViewer.Runtime.Common/12.0.2402.15
Install-Package Microsoft.ReportViewer.Runtime.Common
~ Answered on 2015-07-01 19:42:28