Resolution:
The migrator tool is available from MB3.1.6 and up.
However, please be aware that the migration process is a non-trivial issue. It could be compared to taking code written in a non-object oriented language and converting it into object oriented code.  
The Migrator tool is only a _helper_ tool.  While we expect it to be helpful in migrating the MB 2.5 sheets into MB 3.X transforms, it is impossible to guarantee complete automatic conversion, and we expect at least some manual work will be necessary after running the migrator tool.  In some cases, significant manual work may be necessary and in this case a full manual conversion might be easier and faster.