@ZeeHero9271 A few months ago they were very very rare drops from the first ultimate quests (e.g. Naverious), but I'm not sure if more/better sources have been added since. If you select a quest and choose the "item log" option you can see the frequency of recent drops across all 4 ships.
Just to note, the drop rate in ultimates was so low that you'd honestly be better off farming 600 Rising Weapon Badge 5s than farming ults. Doing Xia's first client order (kill 30 enemies) grants you 5 badges per day which means you can get 15/day super easy across your 3 free characters. And Xia's last client order (complete Xmas UQ) grants 10 badges/day, though it takes a little bit to unlock it so I just do that on my main.
I've also gotten 16-20 RWB5s each time I complete the Christmas UQ on UH and the FF shop has been selling triggers for SG pretty frequently as of late. And if you haven't yet, you can also get badges at certain levels of the current mission pass.