The Yavin Temple Niche decoration can be dropped from Pilgrim's Shadow Packs, which were released on the Cartel Market and bought with Cartel Coins. Cartel Packs, including the Pilgrim's Shadow Pack, include a random selection of items from the Pilgrim's Shadow collection of items. You aren't guaranteed to get a Yavin Temple Niche decoration from a Pilgrim's Shadow Pack, but it is one of the few ways to get a Yavin Temple Niche deco apart from buying it on the GTN from another player.
If you're looking to get a Yavin Temple Niche, 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.
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