Hi Matadem,

re:
> What would be the best way or there is script already to find the center of two curves?

Select the 2 curves, then run Construct > Loft to make a loft surface between them.

Then select the surface and run Construct > Curve > Iso to extract an isoparm from the surface.

There's also a plug-in for it, cmorph from:
http://moi3d.com/wiki/MaxScriptArchive

- Michael