It seems that the only way to convert rfa to adsk, i.e. export Autodesk Revit Architecture data (.rfa) to Autodesk exchange file (.adsk) is to use Revit as no other program likely offers tools for a successful rfa to adsk conversion.
If you do not have access toi Revit, our advice would be to use Revit forums on Autodesk website and ask some user to convert/export the files for you.