These sprites are mostly from Gen VI and Gen VII, extracted from PKHeX (which were pretty much extracted from the main games).
Notable entries that aren't in Gen VII, are Cosplay Pikachu and Spiky-Eared Pichu.
In game, these sprites aren't programmed to have a shiny variation,
and the shiny variation of these sprites were made by msikma.
In Pokemon Sun, Moon, Ultra Sun & Ultra Moon, the Pokedex uses a 2D version of the 3D models, when scrolling through it.
This page has:
1. Sun & Moon's Non-shiny images
2. Sun & Moon's shiny images
3. Ultra Sun & Ultra Moon's non-shiny and shiny sprites on a large image canvas
4. Ultra Necrozma (because it's sprites are merged on the large canvas)
5. Bin files to use with Ohana (there doesn't seem to be a way to mass extract them to .png; has to be extracted manually 1 by 1)
When healing Pokemon in Pokemon Sun, Moon, Ultra Sun & Ultra Moon,
2D sprites of the Pokemon being healed are splashed onto the background of the Pokemon Center's screen, as seen below.
These images are different from the ones splashed on the Pokedex.
This page contains the images extracted from SM Demo, and USUM (for the newer Pokemon).
Older generation Pokemon that aren't in SM Demo are missing from this listing.
(If there's a way to dump all of them straight as images from the garc, I'll do it.
textripper isn't working for this garc <a240 for SM>, and I can only convert the individual bins one by one using ohana presently)
These sprites are from LGPE.
This page hosts a compilation of bag sprites spanning from Gen III all the way up to Gen VII.
Few of these sprites are no longer in Gen VII, as it got replaced by a newer variation of the same icon.