Ok, so after some frustration I got back to what I already had. Went back over the field_groups and over all the fields. When I found that particular fieldname there also were all the sub_fields.
So something like this (typing this out, not copying):
$groups = acf_get_field_groups();
for ($i=0;$i<sizeof($groups);$i++) {
$custom_fields = acf_get_fields( $groups[$i]['ID']);
var_dump( $custom_fields);
}