Original c-source cannot select more than 10 screens, because of the way it gets a screen number. This new code can select any screen.

extended-anything-c-source-elscreen.el

(defun elscreen-get-screen-num-from-candidate (candidate)
  (string-match "\\[\\([0-9]+\\)\\]" candidate)
  (string-to-number (match-string 1 candidate))
)
;; copied from anything-config.el
(setq anything-c-source-elscreen
  '((name . "Elscreen")
    (candidates . (lambda ()
                    (if (cdr (elscreen-get-screen-to-name-alist))
                        (sort
                         (loop for sname in (elscreen-get-screen-to-name-alist)
                               append (list (format "[%d] %s" (car sname) (cdr sname))) into lst
                               finally (return lst))
                         #'(lambda (a b) (compare-strings a nil nil b nil nil))))))
    (action . (("Change Screen".
                (lambda (candidate)
                  (elscreen-goto (elscreen-get-screen-num-from-candidate candidate))))
               ("Kill Screen(s)".
                (lambda (candidate)
                  (dolist (i (anything-marked-candidates))
                    (elscreen-goto (elscreen-get-screen-num-from-candidate i))
                    (elscreen-kill))))
               ("Only Screen".
                (lambda (candidate)
                  (elscreen-goto (elscreen-get-screen-num-from-candidate candidate))
                  (elscreen-kill-others)))))))