Mosin, the Ruger folks generally offer only a few chamberings at certain times, since it costs money to tool up for a caliber. The No. 1s are a small part of the Ruger factory floor, only a few thousand a year get made and shipped.
A few years back, a run of 500 or so were made in .303 British, with at least half of them going to Canada and Australia. So it's pretty scarce here in the US.
The .30-40 Krag version is also sought after. Same with .404 Jeffery. They were offered for a few years a while back, and discontinued.
I think they are missing the boat on not offering some caliber runs, like 7.62x39, 7.62x54r, Swiss, 8mm Mauser, that kind of thing. Guaranteed to sell in steady fashion to shooters.
The .375 H&H is probably the best all-around large game rifle for North America, I think, provided you like single-shot rifles.