Much more Petite Centies are being offered with Flower Stones than all other currencies combined (Life Crystals, Bond Crystals, Flower Medals, Honor Medals). That's 60 pieces (6 stocks with 10 Petite Centies each, restocks every event), for only 600 flower stones.

That's how I got to 100 Petite Centies on the day they were officially introduced. I already refined them into one Centy, and I'm currently sitting on another 70+ Petite Centies.