As you can see at
http://foundation.zurb.com/docs/upgrading.html#upgrading-the-sass
@import "foundation/components/sections";
@import "foundation/components/custom-forms";
have both been removed from the foundation framework. If you are looking to continue using custom forms as defined in Foundation 4 and as described in their official documentation
http://foundation.zurb.com/docs/v/4.3.2/components/custom-forms.html
Then you should probably switch back to Foundation 4.
As an alternative, you could always use CSS3 and pseudo elements to style the checkboxes and or radio buttons without having to use a javascript plugin to do it.