The speaker type is printed on the label on the magnet. It is a Weber Ceramic Signature 8, 4 ohms. You can order one directly from Weber. They are inexpensive, about $33. I haven't found anything else near the price that sounds as good. I have been considering trying an Eminence Patriot 820H which I think should fit. It is, however, twice as expensive.
And of course you can also use the Tode as a head running into an external speaker. We use mine on a 4x12 sometimes and it works quite well.