Dulcet Fancy can be bought in shops.

To fix your problem about Riku's drops, complete Flick Rush cups. These are located in the Fourth District of Traverse Town. Talk to one of the Moogles and you will enter a Flick Rush cup. Doing these will earn you medals and Drop Points so once you think you have enough DP you can just drop automatically. Sorry if this is boring too.

You can get Duclet Fancy from the shop (It's probably once you've already obtained one.) but i'm not sure what world it's from. Probably the Muskateers world or the Sorcerer's Apprentice world. Sorry about the lame answer.

You can fix you Riku problem and the Dulcet fancy one by just playing around with portals (battle portals) cause you get drop points and Dulcet fancy, the portals are in Le Des Cloche and maybe The Grid.

Hope this helps you with both problems :)

Dulcet Fancies are bought from the Moogle Shop (400 Munny), dropped by Ducky Goose and Keeba Tiger, and are found as a chest/award in The Country of the Musketeers and the Symphony of Sorcery at least once each. You can also find some from other enemies unknown to me, and likely as a Portal prize in many areas.