M-x my-helm-for-only-dir

helm-for-only-dir.el

(defun my-helm-for-only-dir ($query)
  (interactive "sDir name: ")
  (helm :sources
        `((name . "helm for directory")
          (candidates . (lambda ()
                          (split-string
                           (shell-command-to-string
                            (format "find `pwd -P` -type d | grep '%s'" $query)))))
          (action . (lambda ($cand)
                      (if (file-directory-p $cand)
                          (dired $cand)
                        (message "It's not a directory")))))))