I don't have one to recommend but how do you plan to use a runtime with FMS12?
Runtimes cannot function as a client of FileMaker Server. You can host a runtime file with FMS12, but then your runtime file functions like any other file, it must be accessed by either FileMaker Pro clients or from Web Browsers (If web published).
Using FileMaker 12 Runtime files with FileMaker Go 12
Home > Using FileMaker Pro Advanced > Using FileMaker Pro Advanced tools > About creating runtime solutions (FileMaker Pro Advanced)
Distributing runtime solutions (FileMaker Pro Advanced)
Introducing Filemaker Runtime Shrinker