Include Typkit in TinyMCE. Don't forget the Kit ID in line 9!

typekit-tinymce.coffee

tinyMCE.init
      setup: ( ed ) ->
        ed.on 'PreInit', (e) ->
          doc = ed.getDoc()

          # Create the script we will add to the header asynchronously
          jscript = "(function() {\n
          				var config = {\n
        						kitId: '######'\n
        					};\n
        					var d = false;\n
        					var tk = document.createElement('script');\n
        					tk.src = '//use.typekit.net/' + config.kitId + '.js';\n
        					tk.type = 'text/javascript';\n
        					tk.async = 'true';\n
        					tk.onload = tk.onreadystatechange = function() {\n
        						var rs = this.readyState;\n
        						if (d || rs && rs != 'complete' && rs != 'loaded') return;\n
        						d = true;\n
        						try { Typekit.load(config); } catch (e) {}\n
        					};\n
        					var s = document.getElementsByTagName('script')[0];\n
        					s.parentNode.insertBefore(tk, s);\n
        				})();"

          # Create a script element and insert the TypeKit code into it
          script = doc.createElement("script")
          script.type = "text/javascript"
          script.appendChild(doc.createTextNode(jscript))

          # Add the script to the header
          doc.getElementsByTagName('head')[0].appendChild(script)