Rem M700's in 'large' calibres are available through their Custom Shop only. There are a few models in assorted "African" and "Alaskan" calibres. .338's and up with 8mm Rem Mag thrown in.
"...Make one..." That'll cost you as much or more than a factory rifle.
CZ makes big bore rifles. Starting at about $1200US.
Like LanceOregon says, shooting big bores is expensive. Think in terms of $75 to $150 or so, per 20.
Guy came in the shop long ago. Said he was going to Africa and wanted his own .458 Win. Bought a Win 70 African and a box of ammo. Picked it up on a Friday evening. Saturday afternoon he was back with the rifle, two empty cases and 18 loaded rounds asking us to sell it for him.
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