Howdy Pard in Norway!
Yes, the best quality percussion (Cap and Ball or C&B) is the ROA (Ruger Old Army). It's not as historically accurate as the Italian colt and remington C&B copies, but is stronger and more reliable. Many of the best CAS C&B shooters here in the US use them. (The stainless steel model with the 5 1/2 barrel, fixed sights, is the best looking and handling in my opinion!)
Is it difficult to get cartridge firearms there? By the way, a conversion cylinder is also made for the ROA which allows 45 LC BP(or smokeless) cartidges to be fired in the ROA. (Remember "Pale Rider" with Clint Eastwood and how he just switched cylinders out in the final gunfight?!)