*Edit: oops that is actually a link form an older dex lol. gimme a sec. okay I can't find a list for Sword/Shield Trade evos for some reason.
Off the top of my head:
-Kadabra, Machoke, Haunter, Boldore, Gurdurr, Phantump, Pumpkaboo = no item required while trade evolving
-Poliwhirl holding King's Rock = Politoed. Kanto Slowpoke holding King's Rock = 'Johto' Slowking
-Scyther holding Metal coat = scizor. Onix holding Metal coat = Steelix.
-Seadra holding Dragon Scale = Kingdra
-Porygon holding upgrade = porygon 2. porygon 2 holding Dubious Disc = Porygon-Z.
-Feebas holding Prism Scale = milotic.
-Rhydon holding protector = Rhyperior.
-Electabuzz holding Electirizer = Electivire
-Magmar holding Magmarizer = Magmortar
-Dusclops holding Reaper Cloth = Dusknoir
-Karrablast/Shelmet. These need to be trade for each other and then both will evolve. No items needed.
-Spritzee holding Sachet = Aromatisse
-Swirlix holding Whipped Dream = Slurpuff
Quite a few of these can be found in the wild actually, during specific weather usually.
The only one I know off the top off my head that can't be found in the wild at all is Porygon 2 & Porygon-Z.