How to add href=”” custom post type?

this would help you do that.. http://wordpress.org/plugins/advanced-custom-fields/
then you can set up the custom field to only show on cptbc_post_type only..

on the template you can then get the value you set on the admin like this:

<a href="https://wordpress.stackexchange.com/questions/108258/<?php echo get_field("field_name', $post->ID);?>">Link</a>