I have an abundance of Calendula flowers blooming right now (you may know these as Pot Marigolds) mostly orange flowers with a few yellow coming in too.
Then drain well before placing on cake. Do this ahead of time so they are sure to be dry.
Original Recipe, on page 17 of Cooking with Herbs by Emelie Tolley and Chris Mead
If you find you are pressed for time, you could use a purchased cake mix and frosting and then add your own flower petals.
I think it would also be nice to use an Angel Food Cake and decorate it with whipped cream, the coconut and the flowers. Or maybe make cupcakes and place the flower petals on each.