Kilibru;
The short answer- Any Juglans Regia walnut is a good starting place for your project. Juglans Regia includes: English, French, Moroccan, Greek, Australian, Russian, Circausian, Turkish,California English, etc.....Where the nut is grown is the name that is associated with the wood.
jjwag69 gave good advise on the lay out,pores, you be the judge of the figure. I have been building stocks for a long time now. I have used almost all of the popular stocking woods. As long as they are laid out correctly I have used them for gunstocks. Again your taste in wood is important. Lay out and grain flow are MOST important...NOT which walnut it is.