right now, they're on pages 5 (orangeberry) and 6 (everything else) of
the item database's adventuring loot query. seasonal availability is in the top right of each item "card"
the SON exclusives are orangeberry (spring/summer), ashroot seeds (autumn/winter), crimson shieldplant (spring), lavender canopy flowers (summer), bitter acorns (autumn), whiskershelf fungus (winter), and vial of null aspect (all seasons)
most jobs have special winter resources. of particular note is snowspider silk, used to craft the glittersilk apparel. it's gathered by bug catchers. there's no way to view crafts by season so i've complied a list for you below by hand
there is also:
gatherer - large crunchy leaves (used for the haunted buildings)
bug catcher - silver fireflies (used to craft
mage's compendium)
bug catcher - snow ants (replacement for crickets for bakers, used in some luncheon recipes)
gatherer/herbalist - snowcap mushrooms (used in some luncheons i'm pretty sure)
farmer - starfruit, snowpeas, snowmeowtoes (used in some luncheons and crafts)
bug catcher - snowspider silk (for the glittersilks)
herbalist/gatherer/apothecary - wintermint (used for a coloration of glittersilks and as a replacement for chamomile)
gatherer - fallen meteorite (no use currently afaik)
gardener - crocus, not-holly, forget-me-not (all used for crafting decor and glittersilks)
gatherer/herbalist - silverseal (used in decor crafts)
gatherer/herbalist - walnuts (used in many crafts, including glittersilks)
you can also find a lot of these through adventuring, and a few adventuring exclusives:
winterberries - used in a luncheon iirc
frostdew flowers - no use currently
there's also a bunch of related decor and clothes that can drop but i uh. am not listing all that