While I'm not entirely certain that this isn't just me failing to understand something, it seems as though there are a number of event cosmetics that simply aren't appearing for sale in the Market.
A clear example, shown in image #1, is that of the fondue bins in Tropicvale Treats -- themed like wrapped gifts complete with holly.
Image #2 shows the portion of the shop where I was previously able to buy non-character event cosmetics, but after getting about four of them (all exterior items, as I recall), no more have appeared. I now have over 6k of the event currency sitting there unspent because there's nothing to buy with it.
If this isn't a bug, then I'm very confused about what the point of all this extra event currency from puchasing the pass is...
This has been reported by a lot of players and we are currently working on a fix for this. Thank you for letting us know!