PT6A:
Is there any company out there that takes on this kind of task for areas of the world that are not fully charted?
Airport Performance Group:
http://www.apg.aero
and
Jeppesen
How complete either of them are is open to conjecture.
As John says, getting on site with the correct equipment is the only fool-proof method, and even that is problematic without repeated surveys at fairly short intervals.