Items that come with merchandise are never offered for sale on the Mogstation separately because it defeats the whole purpose of having such ingame items in the first place - they're there to encourage sales of the merchandise so that SE can break even on the expense of producing them, so if those items were later offered separately, it would affect the sales of merchandise (and I'm not being derogatory here, I actually like having items with merchandise, as it's a nice bonus for buying something like a soundtrack or artbook).

Yes it's unfortunate that some items are now unattainable, but that's life is it not? There will always be situations where something is only available a short time and once it's gone, it's gone forever.

As for the 30th Anniversary of FF, didn't SE already do a series-wide celebration a couple of months ago? (Online video with interviews with various SE staff talking about the series, it's past and possible future directions, including Yoshi). I think if SE were going to do a '30th Anniversary' event in game it would have already been announced by now. I guess though it's entirely possible this year's 'Rising' event in August (which celebrates FFXIV's rebirth from 1.0 into ARR) may have some extra connection to the 30th Anniversary. But that's just my own musings so take from that what you will.