These aren't exactly new actions, but new-ish.

Assuming you want control round feed, Winchester is making their updated pre64 model again. Just buy one in 375 H&H and have it rebarreled, magazine modified, and blue printed.

Ruger has also updated their Safari Magnum, which is available in 416 Rigby and 458 Lott. It also comes with a very very nice piece of wood. Ditto: just rebarrel, magazine modifications, and blueprint it.

CZ is making the big Mauser action, the model CZ550. I have one in 416 Rigby and I am very happy with it. This action is long enough for the Gibbs, too. However, it does have the hogback stock on it, and some folks don't like its appearance.

The nice thing of using these approaches is that you could choose a custom barrel, and since the rifle is blueprinted and you would assured of it shooting quite well.

Olympia does make a very nice action, but it is very expensive. I haven't priced one in a few years, but I found that I could buy any of the three rifles above, have them blueprinted and rebarreled in 416 Rigby and top it with a Leupold VX-III with Warne Rings for about the same price as the action alone.

Or you could go with some of the full custom actions that various gunsmiths make which have extablished a name for themselves. I know of several, but I don't know if they specialize in DGR. I do believe Dakota makes several DGRs and they do have a fine reputation. Searcy is another. Both have websites, if you want to inquire.

BTW, keep in mind the Gibbs is a 0.505 bore and the 0.510 bore is very common today. Thus, bullets are harder to find in the 505 caliber. You might opt to have the 505 Gibbs made into a 510 Gibbs. Clearly, you can't buy off the shelf ammo for it, but you could use the load data directly and work up. Since the exapansion ratio is higher, you might get a bit more velocity for a given bullet weight, too.

RobertD