Hu,
Do you have a CMM?
If you do, there is software out there that you can use to collect a "cloud" of points from you model then import them into you cad system.
The other option would be to sub the work out to someone in your area.
I have a small CMM that I use from time to time like this , but other times I will send the model out to have it done.
I don't do much work like this, so if I had it to do over, I probably wouldn't have spent the money on the software to do it.
I would sub the work out to someone who makes a living at it.
JMO
Ward