BudsGunShop.com - Cerakote?

it is factory however it is no longer listed by Glock with the FDE color so it appears to be a discontinued model

Crystal, OEM Factory. I would check on large gun and accessory sites like (6)un (8)roker and Guns International as discontinued and hard to find firearms and accessories show up for sale by private individuals and small shops. Just replace (6) & (8) with G & B. --------------- gunsinternational.com/

Like Randy said it's done in house but looks to be discontinued. If you want to find one your best bet would be to try gunbr0ker, they're a site that allows private owners and small shops to sell their products so they usually have rare and hard to find firearms and accessories. Hope this helps.