create-scratch-buffer

buffer-defuns.el

(defun create-scratch-buffer nil
  "create a new scratch buffer to work in. (could be *scratch* - *scratchX*)"
  (interactive)
  (let ((n 0)
        bufname)
    (while (progn
             (setq bufname (concat "*scratch"
                                   (if (= n 0) "" (int-to-string n))
                                   "*"))
             (setq n (1+ n))
             (get-buffer bufname)))
    (switch-to-buffer (get-buffer-create bufname))
    (emacs-lisp-mode)
    ))

How about this, letting Emacs uniquely name the buffer for you?

(defun create-scratch-buffer ()
  (interactive)
  (switch-to-buffer (generate-new-buffer "*scratch*"))
  (emacs-lisp-mode))