You will need to get the original files from the creator of the model. You can't go from realflight to 3dsmax, only 3dsmax to realflight with the max exporter.
Another option is for you to create the model yourself. Do the mapping, pivots, colorscheme, and physics. There's plenty of help here, you will need a very old version of 3dsmax 2012 32bit or an older version of Blender.
That's the only options. Yes you still need the old version of 3dsmax. We do expect a new exporter though after RealFlight 8 is released.