There are some old items, like "Pumpkin Patch" items or Fireside. Do those get reintroduced in seasonal shops like the items from the Brewery? Or is it there something else I should know about these items?
You can get old Pumpkin Patch items from the Pumpkin Patch during Morostide and old Fireside items from the Bonfire and Charity during Fireside.
Oh, alrighty! What about old Melody items? Are those obtainable as well?
We usually have a Free Shop event soon after Luminaire and Melody items can turn up in there.
sometimes, during the event in question, one of the questers will have a chance at giving out old event prizes as well. Its generally announced in the news when they do that.
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We haven't been getting much in the way of Free Shop released Melody-items recently. has spent more time controlling what goes out via Free Shop in terms of filling it up and what she allows it to have, so it's not nearly as nice as it used to be. I would not rely on it myself anymore.
When quest grantors do give out old items they are not necessarily given out by price/rarity/demand, so you may not get what you want or even anything valuable. Of the item you want, from other users who luck upon it and don't want it, the price in their shop may not drop all that much. This is because each grantor might drop only two or three items out of all their quests, the total number of items re-released is not huge compared to demand.
The Patch/Bonfire/Freyalise having old items is usually limited to the most recent years unless staff tweaks them. I have mostly seen this with the Bonfire. Charity used to retire her old items but no longer does that I can tell.
So what shall I do if I look for all the collectable pieces of old items? Such as books and food, Should I just buy them from people?
- do you know Subeta Lodge?
Subeta Lodge lists all these items for you.
Normally, during holidays (and sometimes during site anniversaries, etc) these items are given out in quests, so be sure to do all of your quests during Fireside, Morostide, Luminaire, and similar holidays. Also, Quentin gives out a lot of old holiday items, especially Morostide items. If I can only do one set of quests on a given day, I make sure to do Quentin. Quentin also gives out the mage amulets, which sell for over 300K SP in your shop. :)
Many of these holiday items have been given out so frequently that you won't lose any SP if you do buy them up now, so a good thing to do is use the search function on Subeta Lodge. Anything that is under 5000-10000 SP you might as well just buy if you really want it.

I have no good general advice for you on this. In the end, nothing ever retires in Subeta permanently. How much of a hurry are you in, and what would you spend your site currencies on else?
SubetaLodge does track the prices of these items. Most of these items are called for by NPCs Quentin and Cinthia. If they cost more than 50K, then all the spares of them have already been turned in for those quest rewards, any that have been released via the other methods listed here have also been turned in, and IMO the price will likely go up. OTOH I hoard like mad, so if me or someone like me has a ton of them in their shop, it won't and you can wait.
Once the market price of an item gets high, then suddenly users and staff care a great deal about "preserving value" and these items become less likely to be released in any easy-to-get way in the future. Which ones get picked that way? shrugs My best guess is that if I really wanted to know I'd go back through all the Suggestions and see how the wind blows for whatever I was looking for.
Nobody will know for sure what overall effect The RIFT in the Galaxan Wastes will have on the retired item prices of items that are already very high-priced, it's still very new. So next year the picture could be very different.