Cramorant has two locations where it can be found. It can be found as a pretty frequent random encounter in Circhester Bay which is located on Route 9 which is well past the Fire type gym. You can also encounter one in the Wild Area more specifically in the Lake of Outrage only appearing in rainy weather rather commonly. Both of these places are inaccessible before the third gym which means it's not likely to catch one. There are however plenty of options in Galar Mine No.2 which provide excellent Pokemon to help you defeat Kabu such as Drednaw, Shellos, Corphish, and Barboach. All of his Pokemon that he uses share a weakness to both water and Rock making Drednaw an excellent choice!