those .vrscene can be purchased at Maxtree for example.
Simple but very crucial workflow point.
Without this possibility (of scattering), Rhino users (like me) need to dowload fbx versions instead, and set all texture maps and setting propoerly for each species used.
In vrscene objects provided though (every material is already set and vrscene are ready to use).
this idea has also been suggested here :)
https://forums.chaos.com/forum/v-ray-for-rhino-forums/v-ray-for-rhino-wishlist/1129394-vrscene-support-on-the-new-scatter-component