I have purchased aluminum anodes from these guys:
https://www.boatzincs.com/use_milspec_a18001k.html
they discus milspec anodes there
great service
Agree. I had a 20 minute discussion with a boatzincs employee just minutes before I saw this thread. He convinced me that aluminum was the way to go for both the saildrive and prop anodes. We will see. I scrub my bottom weekly and will monitor them.