Is it the same vendor as the other prisms such as the bubbles, pedals, etc.? Because I have Platinum Plan and there's none for sale.

"Couples who selected the platinum plan can also purchase the special Magicked Prism (Hearts) ceremony favor."

It says that on the Eternal Bond Page but I've yet to actually find any vendor near by the church selling them.

( Scroll down the page and read Ceremony Favors section for info. )