You'd need a really long head tude in order to use a really deep star nut. If you can deal with installing the fork and stem without the star nut (much more difficult to get proper preload) a quill stem CAN be used in a (steel) threadless fork.

With the right tools many (not all) threadless forks can be converted to threaded. If you do a forum search you should find the relevant info. The install depth for the quill should still place the wedge in the head tube, so you'd need a fairly tall stem, but that's not that unusual an item.