Hey @pandac, the Charm-Store (cs) was switched off on the 9th of February and all the charms were transferred to the brand new Charmhub.
containers-metallb is now listed here and you can deploy it with
juju deploy containers-metallb
At the bottom of MetalLB | Ubuntu, you can see a link to edit that page. Can you please make a comment there so folks can adjust their instructions?
Let me know if I can help you with anything else 