If you're trying to lose weight, you ought to skip the sour cream and butter and just grill the steaks. You're actually probably just fine on selenium (especially if eating grass-fed; if not, it's in the liver at least) and potassium (there's a huge amount in meat). There are no carnivores that don't produce their own vitamin C, so just take a supplement if you're going to avoid carbs. Sure, some populations of hominins in or around glacial maxima squeaked by with the trace amounts on freshly killed meat. Odds are you're not eating fresh kills mostly raw (and probably want to have optimal health rather than the bare minimum to avoid disease like scurvy), so just take some vitamin C. Scurvy takes a long time to develop and is pretty nasty by the time you would notice it.
It's far more likely that you're deficient in magnesium than calcium, so you're going to want to supplement with that as well. I would also be concerned about essential fatty acids, vitamin E etc., which could be had from eating (especially pastured) egg yolks. Replacing the butter and sour cream with whole eggs/egg yolks would be far better for your nutrition.
If you feel well aside from the keto breath and are losing fat (assuming that's your goal) then keep going with what you're doing. If your fat loss stalls, you're going to want to trim the steaks, eat less at a time (like half a steak, wait until you're hungry again, eat another half etc.) and/or do more walking.