Drop a line to Welsh Government, perhaps they'll send you a personal invite if they have another one.
Seriously, what more than advertise it on the BBC Wales website and the local Welsh Newspaper website, along with Welsh Radio could they have done to advertise it? Mainstream BBC were never going to advertise it because it was irrelevant to them. If you want to know what's happening in Wales listen/watch/read programmes/articles relevant to Wales.
I knew about it well in advance, and took the conscious decision that it was irrelevant to me, so did not attend.