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You could get your local sports store to see if any are available in NZ but don't think they would have one in 338 Lapua but you never know.
I got my 300 Win Mag one direct from RCBS in the USA.
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So long as they chamber and close there should be no problem firing them, essentially you would be fire forming them to your chamber. You could load those tighter ones down a bit for the reforming...