grand veneur
AH elite
Chiming in from 2024.
The trend continues for the diminishing of true magnum-length actions being available in mass produced rifles from the "big guys".
The Sako 85 line has since fallen to the same fate as the CZ550's, being the last of the affordable XL magnums available to the average working man.
Like others have commented there are still plenty of offerings that will fit the 375HH, 416 RemMag and the 3.34 Magnums, however if you're in the market for a 416 Rigby, 450 Rigby, 505 Gibbs etc. you're now looking at 5 figure Mausers, Heyms, Parkwest Arms and the like.
The three cartridges you quoted, meaning the 416 Rigby, the 450 Rigby and the 505 Gibbs, were traditionally found primarily in expensive customer rifles. A few cheap attempts have been made to offer this cartridges in cheaper rifles, but if all of these companies now stop producing such rifles, the deal probably was not worth it. If you read the posts on the forum concerning the use of calibers for big game hunting, the trend is towards much smaller cartridges, especially and above all the 375 H&H Magnum, which does not require a magnum system. There are also plenty of cheaper alternatives to the three cartridges mentioned that do the job well and that don't require a magnum system. Magnum systems will continue to be manufactured but primarily for upper class custom rifles.