Hook: Ceiling HookThe Holocron of Despair decoration fits into a purple ceiling hook.
How to Get a Holocron of Despair Decoration
Cartel Pack Decorations
The Holocron of Despair decoration can be dropped from Oppressor Alliance Packs, which were released on the Cartel Market and bought with Cartel Coins. Cartel Packs, including the Oppressor Alliance Pack, include a random selection of items from the Oppressor Alliance collection of items. You aren't guaranteed to get a Holocron of Despair decoration from a Oppressor Alliance Pack, but it is one of the few ways to get a Holocron of Despair deco apart from buying it on the GTN from another player.
If you're looking to get a Holocron of Despair, the easiest way to get it is to head to the Galactic Trade Network (GTN) in SWTOR and buy it with credits from another player. If it's very rare and not available on the Cartel Market, you could try buying from the GTN and hope you get it.