This is a mass produced piece with a chromed blade and a plastic scabbard and hilt. The "stone" is glass. Made for the market. Could have been made last year. The mounts are molded plastic (or possibly copper) coated with some kind of silver looking stuff (not real silver).
The old ones, even from the 1930's, have leather covered wood scabbards with brass or silver mounts (sometimes with silver marks on the back). The old hilts could be made of silver, ebony, or horn, and hand carved or hand chased.
Sorry for the bad news. I have many of these sold over the years and have owned some older true sgian dubhs (one of which I which I had kept!). And yes these are used today for wearing in the top of the stocking in formal traditional Scottish mens dress with a kilt (nothing underneath the kilt!
).