Your question assumes the truth of 'sola scriptura', which people in the Catholic and Orthodox communions have never held.
Good point.
But even so, the Scripture referenced tells me only that touching Elisha's bones can bring a dead man back to life, not "The bones (of those whom the Catholic Church call saints.) are holy, sanctified by the righteousness of the saint to whom they belonged."
That's a pretty big leap.
It is only a leap if that is all the data you have to go by. But if you study early Church history, you see many testimonies concerning the healing power of the relics of the saints. St. Augustine, for example, talks about people being healed as the relics of saints are carried through the streets on feast days.
-A8