What version of RapidWeaver are you using?
MetaMate I think was taken over by @joeworkman, at least I read that on a old post from @zeebe who at the time worked for Joe. I don’t think it ever got updated.
Seydesign was taken over by @willwood, he had upgrade instructions on the seydesign website.
In any case I’m not sure why these addons aren’t showing up in the addon manager. Have you tried looking for them in finder?