There's a rotation of two weeks for specific archaeology digsites in specific zones. For example, if you're missing demonic pristines, you'll have to wait until demonic digsites are up in either Azsuna, Stormheim, Suramar or Val'sharah.
Demonic Archaeology - Azsuna, Stormheim, Suramar or Val'sharah:
Pristine Flayed-Skin Chronicle
Pristine Houndstooth Hauberk
Pristine Imp's Cup
Pristine Malformed Abyssal
Pristine Orb of Inner Chaos
Highborne Archaeology - Azsuna, Suramar or Val'sharah:
Pristine Inert Leystone Charm
Pristine Nobleman's Letter Opener
Pristine Pre-War Highborne Tapestry
Pristine Quietvine Vial
Pristine Violetglass Vessel
Highmountain Tauren Archaeology - Highmountain:
Pristine Trailhead Drum
Pristine Hand-Smoothed Pyrestone
Pristine Stonewood Bow
Pristine Moosebone Fish-Hook
Pristine Drogbar Gem-Roller