In Pokémon Sword and Shield’s Crown Tundra DLC, you’ll have the opportunity to get a Galarian Slowking.
Galarian Slowpoke are originally found around the Isle of Armor and evolve into Slowbro using a Galarica Cuff. If you want a Slowking instead, you’ll need to use a Galarica Wreath. Just like the Galarica Cuff, you’ll need to trade Galarica Twigs for it.
Galarica Twigs can be found sitting under trees on the Isle of Armor and the Crown Tundra. Just look for a sparkling object under the trees as you explore, and press A to pick them up.
The NPC to trade the items with is in a cave in the Roaring Sea Caves area. However, you’ll have to cross through the Frigid Sea to find her. To get there, stay on the lower part of Giant’s Bed, avoiding going up any cliffs. This will eventually lead you to Giant’s Foot, where you can enter the Roaring Sea Caves on your bike. While in the cave, keep heading to the east until you are in the glacier-filled Frigid Sea. Upon exiting the caves, you’ll see a river. Get on your bike and head left down the river to find the NPC.
You’ll need to trade her 15 Twigs for one Wreath. After you get the Wreath, just use it on a Slowpoke to get your Slowking.
Galarian Slowking is still psychic-type, but it’s also poison-type, rather than Kantonian Slowking’s water-type.