All I can suggest is a Faro Arm. You can get them in 10' lengths (maybe 12') and they cost a lot of money ($30K). I used the platinum- I'm sure the Gold and Silver are cheaper. You'll probably need to leapfrog with the arm, but the accuracy should be fine for your purposes.
As I recall it came with surface creation software that worked with Cadkey (now KeyCreator) to create NURBS surfaces. Worst case you can generate points.
This is not a simple thing you are looking for - so maybe you've got the money to spend.