As mentioned earlier BSA back pre WW1 seems to have used premium / better walnut on some guns that were given as prizes, and I have seen enough (not many but maybe double figures) guns with shotgun grade Walnut that it may have been the case that you could ask for a better grade of wood (they would fit any sight combination / various stock styles / lengths) It seems only logical. The majority of buyers at that time would have been happy just to have the latest gun at a fair old cost to start with , but even then there would have been well heeled types who would have wanted the best I would say personally.
I am lucky enough to have this example;
https://www.flickr.com/photos/312284...7607860743867/
https://www.flickr.com/photos/312284...7607860743867/
As you rightly say about guitars (I have a couple of nice ones) just say a bookmatched Sikta top can be several hundred pounds as an option, and don't even think about old pre ban felled or cites Brazilian rosewood
ATB, Ed