If you are doing the quest I think you are, it is an extremely low drop rate for those quest etcs. Keep trying
If thats the case I suggest for an adjustment for increase of drop rate for silk feather, because Sakura Cellion has a bs low spawn rate
They do not drop the silk feather, only jr Lioners do. I've done this quest numerous times for Quest Virtuoso, I don't think hiddenstreet reflects on it but I know it's around in the community: Edit: Tried to add a link but it keeps changing it into media.... Google silk feather pre bb and there will be a reddit post saying the same thing!
I've always finished collecting them by the time I finished collecting all 5 cards, sometimes I'll only have 3-4 cards. I think it takes 10-15min if you're 4th job and a bit longer if you're doing it around the recommended level. I don't think I've ever spent longer than 25-30min farming for them though on a lower leveled character.