DH makes both a coconut and pineapple cake mix, so you can always look for those.
That is one of my favorite flavor combinations.
When I do it I will either do a coconut cake with pineapple filling and usually coconut flavored buttercream or a pineapple cake with coconut filling (usually buttercream with some coconut mixed in) and some coconut buttercream.
This is the pineapple filling I have used...
3 Tablespoon all purpose flour
½ cup sugar
2 Tablespoon butter or margarine
20 oz crushed pineapple undrained
Combine flour and sugar in a small saucepan, add pineapple and butter. Cook over medium heat, stirring constantly, until thicken. Cool.
Yield: 2 2/3 cups