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