Subetalodge doesn't have much info on these items. Some I'd expect to be holiday items or game prizes, but they're not labeled as such and don't have the appropriate rarity. There's no shop source either.

I'm sorting my wishlist and vault and trying to find where to categorize these. Yes, I sort things as entertainment. 🤷

I'll probably wind up finding more to add to this list as I come across other things, so feel free to add to it if you find more stuff lacking info!

I think most, if not all the retired christmas/mother's day/etc items with a shop price were from the old Holiday Shop. I remember buying the snowy village items from there anyway. To verify you could just check the months of the relevant holidays throughout the early years to when they were added to the shop. Though the archive doesn't go all the way back unfortunately.

Some examples:

The Sufganiyot items were added on December 16, 2006 to the Bake Stop. December 2006.

The patriotic items were added to various shops. The sucker and taffy in July 2005, added to the Candy Shack. Same with the following year, July 2006, then the aromatic apple pie (Bake Stop) and sundae (Icy Goods) gets added.

Candy Kraken was added October 6 2006 to the Minions Market. October 2006.

April 5 appears to be Kumos Day. April 2006. It's not in the news post, but the Bloodred Kumos Doll is close in ID to the one in the news post. I'm guessing they were all released at the same time. They were in the Toy Box.

King Keith's Cake I think was added on June 1 2005. It seems to have had its name changed, since it says "slice of keiths cake". There's no item called that, and Slice of King Keiths Cake has a close ID to the candle in the news post, so I think it's the same item. Art seems newer too, so probably revamped later. It doesn't actually say in the news post where it was added, though. June 2005.

Before looking I didn't know so many seasonal items used to just be added to regular shops. I might look some more later, always love looking through the news archives but it does take a bit of time to trawl through.

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The goops I know come from the pet zapper when it zaps one of your items, you can get either dust or goop. But I think I remember a thread where someone said they hadn't gotten some of those in a while so they might not be going out at the moment?

SPOILER (click to toggle)

Tried looking for news posts for Kess and Seed. Kess I think based on the itemID, was added before the archive starts. Several other minions which are found in the Minions Market were added around the same time, so that would be my guess (no guarantee it was that, though). Seed, I found news posts with items released around the same time (June 2005. Here's the relevant page in the Item Directory where it was added), but no news post for Seed. SL does say it was related to the IRC, and there are mentions of an IRC here and there. Between the release of the fake pet tails and earrings, there was a trivia but I think it gave out Maleria Plushie. So a real mystery item! There's also the other IRC item, the mIRC egg/bunny, which seems to have been given away (randomly?) for chatting in the IRC during easter. See the news post for when Seed was added to the crystal shop later, and from there the linked news post to when the IRC stopped being supported and people were commenting asking how to get the mIRC egg now. I couldn't find a news post for the mIRC egg either (March 2005, when surrounding eggs were added). So it seems all three items were not announced in the news when they were added. Maybe someone who was around back then or was in the IRC remembers how you got it.