Well, low and behold, there ARE internal anodes on the BF 200 and BF 225. Thanks to Keith Whelan at Whelan's Marina in Farmham, Virginia. There are two of them located under each exhaust manifold and are clearly shown on Page 5-119 of the shop manual. Keith says the part number is 12155-zv5-000.
There is no mention of their replacement in the Honda maintenance schedule. On page 5-119 it simply says "replace the anode metal if it is corroded excessively." Of course, you must remove the entire exhaust manifold to inspect them. Great design, Honda! It would have been much more maintenance friendly if they had thought about making them a bolt-in anode, accessable from the outside of the manifold.
There is no mention of their replacement in the Honda maintenance schedule. On page 5-119 it simply says "replace the anode metal if it is corroded excessively." Of course, you must remove the entire exhaust manifold to inspect them. Great design, Honda! It would have been much more maintenance friendly if they had thought about making them a bolt-in anode, accessable from the outside of the manifold.