The Accessory Socket Stone can be obtainable from BH quests, TM Lunar, FSP Exchange, CTF, Heroic...if i find out more ill add it.
The higher the amount of Accessory Socket Stones you use, improves the success rate.
After your 1st socket, the NPC will eat up your socket stones, so don't be stingy pay up!
1st Socket= 3 Stones
2nd Socket= 15 Stones
3rd Socket= 36 Stones
4th Socket= 75 Stones
129 stones for all 4.