Re: .338 lapua ai/improved
You can order a matching resize and chamber reamer from Dave Kiff at PTG. Cost is about $135 each for the 338 size.
However, when you consider this should be a one time thing for the resize reamer, and I am not sure the cost of the reamer, chambering the dies, die blanks, heat treating etc, it is cost effective for the one time user.
consider going to Neil Jones at Neil Jones custom dies. He can make a set of dies perfectly matched to your chamber for around $350
I would still recommend the chamber reamer, that way your next barrel should match your existing dies with only resetting the shoulder.