I got tired of paying the exorbitant price
for the Flex-O-Fold anodes and made a simple modification which allows the use of generic "donut" zincs in their place.
All it takes is countersinking the three screws that hold the plate onto the hub, and buying
three countersunk head
allen screws to replace the cap screws that come from the factory. Then by putting a flat washer on the central screw that holds the anode on and tightening it up, Bob's your uncle. This has worked for us for the past 6 years.
The donut zincs don't have quite as much mass as the factory ones, but on our boat
they easily last between slippings. The price
differential in Oz is two donuts for about 12 dollars vs around 50 for one factory job.