That link is indeed the best place to find old eBulletins. It should remain accessible indefinitely, despite recent changes to the BAA’s mailing lists.
There used to be an alternative archive here… <britastro.org/ebulletins>… which is probably the one Nick was thinking of, but it’s no longer advertised asn nobodywas updating it.
I don’t know what archival plans anybody has for the new email lists.