Combi's & Drillings are very popular over here in scandinavia, especially for hunting roe deer with small dogs where you are also permitted to use the shotgun.
I have a combi in 12 / 7X57R and I'm very happy with it, it's only a cheap mass produced Sabatti but it's shooting into an inch at 100 meters with ease, it has the rifle barrel welded to the shotgun barrel so after a several quick shots it can begin to shoot high. You can also get them with a free floating rifle barrel but I prefer the look and the sturdiness of the attached. I prefer it to my rifle when out stalking as if something else should present itself, a hare, grouse or capercaille should present itself I can have a go with the shotgun barrel. I have a 1.5-6x42 scope mounted on mine and you can still take birds on the wing with it, you just need to practice a bit on clays to get used to it.
As for ammunition, I know that Sellior & Bellot and PPU Prvi Partizan load in these calibers at reasonable prices and the brass isn't too bad either, Norma also load but over here in Norway they are really expensive. Regarding the dies, I know for the 7X57R you can use the ordinary 7X57 not sure if that applies to the other "R" calibers though.
I see on guntrader there are several up for sale.
Here's a few pics of mine:
Go on, buy one