Another way to get An Omnium Star Lost Ark Gold is to purchase one from the Spearfish hunting Guild Vessel in Punika. If you set sail at the Punika docks, there is the possibility that a commercial ship named the Spearfish Hunting Guild Vessel will be there to offer this Omnium Star. The star is sold in 8000 Sun Coins, which you can obtain from Sailing Voyages or High Seas Coin Chests. If you're not able to fill chests like these, you can complete island quests or Procyon's Compass island adventure to gain more.
If you've got plenty of Rapport items to give to NPCs, reaching the Trusted Rapport ranking with Nia will be another method to earn the Omnium Star. However, once you get to Friendly level with her you will require high virtue stats in order in order to progress to Trusted. One way to get around this is by achieving Friendly Level One with Nia and then giving her legendary gifts so that you can skip Friendly level two and skip to Trusted level. For example, if you are at Friendly stage one alongside Nia and have 7000 points in your account, then you can give her 13 legendary gifts for her to skip Trusted. However, gaining trust with Nia is a lot more difficult even without this method if you do not have the necessary virtue statistics to move to Trusted.
In addition, you can earn an Omnium Star from completing the Purification Ceremony daily Una task. While the actual task isn't too difficult to complete, it will take 21 days in real life to finish. It is important to begin this as early as possible in order to earn the Omnium Star quick. Fortunately, you can get another Omnium Stars in between these activities.