Custom dies can be made by Neil Jnes.
I just ordered a custom trim die from him.
He can make about anything and is very helpful to get you satisfied with the dies you need.
He isn't cheap, but I guess I can tell you in a short while about the quality of the dies he makes.
One of the things which tells about his precision is that he asks you to send in three cases for getting the best possible fitting.
If you plan on doing so, I would suggest you to fire some factory ammo, and send these cases to him.
you can find him at
www.neiljones.com