Try this script. http://www.scriptspot.com/3ds-max/scripts/vertex-normals-stitcher You can also create reference mesh (duplicate separate meshes, attach them together, weld vertices). Then use normal thief script to copy normal direction from reference object to each target.
I tried the first one. It seems to do something weird to the normals. This is how the original model looks: This is how it looks after using Vertex Normals Stitcher: When I add the modifier Edit Normals to look what's happening, it seems to fix itself: But as soon as I move the model to another pose, this weird behavior…
there are other scripts on scriptspot, maybe try this http://www.scriptspot.com/3ds-max/scripts/average-copy-border-vertex-normals just search a bit there are a couple of tools
if in Max it doesn't work as expected , try Blender Data transfer modifier ( same idea as with normal theft script) to transfer normals from other model without seams. Imo it works just ok. Just don't forget to set auto smooth before applying.…