As a long-suffering left-handed shooter, the topic of trying to get exactly what my heart wants (logic be damned!) is one of my favorite quests. I've spent a lot of time looking for obscure left-handed unicorns. Unlike you, I found the 458 Win Mag to be more than sufficient for my intended needs. In one of your previous posts, I had mentioned the 404 Jeffery above (but forgot it was you who started the 50 cal thread) & the possibility of finder a larger LH Weatherby. So here's some additional thoughts.
Certain chamberings with large African cases can have challenges when trying to rebarrel smaller left-handed rifles to feed the cartridges properly. You either have to go custom or possibly pay a gunsmith a lot of money to get them to work well. So I was always a bit leery of chamberings with .585+ bolt faces because I worried I might not have the financial resources to end up with the rifle I really wanted. The
$10k Heym in 416 Rigby that sold in the Classifieds recently is about as good as it gets sometimes. Occasionally, I'll see the rare left-handed 416 Rigby go for an "affordable" $8,625 like the one below but once you add a buyer's premium, tax & other fees, you're over the $10k threshold pretty quick.
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A few years back this Dumoulin 416 Rigby sold for $6,600 including the buyer's premium but that's a rare instance of a nice LH rifle going for a good price. You have to be really patient to find one of these.
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I like my LH Winchester M70 Safari Express in 375 H&H a lot. It's a great rifle for less than $2k. If I wanted to upsize it, I might get
Pac-Nor to make me a .475 barrel chambered in 470 Capstick. If I didn't reload, I can still
buy ammo for it that produces some impressive energy. I'm assuming the recoil would be significant as well. I'm sure you could accomplish the same thing with a CZ, Zastava, Heym SR20G, etc.
There's a pair of them coming up for auction this weekend (
Rifle #1 &
Rifle #2) that could possibly be used as a donor to base an affordable larger build off of.
There's a
LH Dakota 76 in 450 Dakota available for $7,500.
Parkwest will build you a left-handed rifle but for $8k you can only get it as big as the 404 Jeffery or Dakota. In order to get the larger calibers you mentioned you have to spend $12k & get the Dark Continent model. The proprietary Dakota chamberings are impressive but the lack of brass & ammo is a concern.
As I'm sure you well know, creating left-handed, magnum-action, CRF rifles with big bolt faces while not breaking the bank can be difficult. But I never want to discourage anyone from tilting at this particular windmill.