Here’s a quick solution if your WordPress custom post types (CPT) aren’t available for selection in the menu editor:
In the menu editor screen, at the top right is a “Screen Options” drop down, click on that and check each CPT you want to be able to add.
If your CPT isn’t there, goto the CPT declaration file (functions.php if you lump all your code together, tut) and ensure each one has the following set:
'show_in_nav_menus' => true
If that doesn’t work then you’ve really broken it, tut tut tut.