Hi there,
It looks like there is a Maya plugin for the Havok physics engine (which is what Reactor is inside 3ds max). 3rd section down on Autodesk:
https://www.havok.com/content/blogcategory/30/68/
also mentioned here:
https://en.wikipedia.org/wiki/Havok_(software)
I think you'd need to contact Havok themselves about seeing how you can obtain it.
https://www.havok.com/
Simon