No known way to get this in the game yet.
Contents(One pick from a pool)
ItemQuantityChanceFor
Refining Stone (Bound) x1065%Level 1 - 100
Expert's Refining Stone (Bound) x1025%Level 1 - 100
Artisan's Refining Stone (Bound) x108%Level 1 - 100
Artisan's Ultimate Refining Stone (Bound) x102%Level 1 - 100