Keites is a High elf vendor who can be found in the Alchemist hall which is in the north western part of the city of Velika closest crafting building to the banker in that area. Keites is labeled with "Alchemical Materials" Note: this mat is on the second page of Keites inventory.
There is a crafting quest you can get after first coming to Velika, requiring you to make 25 Eggshell powder. which requires 25 Basilisk Egg shells (provided by quest giver) and 25 Apprentice's Catalyst. The cost of materials to complete this quest amounts to 6 gold.