To get to Blackthorn City, you must defeat (or catch) the red Gyarados and find Team Rocket's hideout in Mahogany Town. Then head east to Ice path. After that youre in Blackthorn City.
you have to get through the ice path
you have to solve the team rocket problem in goldenrod city's radio tower. N
You can get it in Dragons den in black thorn city.
Go to black thorn city and there will be a man in a house who will teach it to only these pokemon. Charizard typhlosion blaziken
You have to go to black thorn city. There is a guy there (in one of the houses) who will delete moves for you.
castelia city
At striaton city
Clair is at black thorn city but first you need to get through ice path and route 44
You need to defeat Team Rocket in Goldenrod City.
at black city area and route 18
im answering this from memory but you have to beat team rocket in the poke mart and then he will be gone. but im not completely sure so if I'm wrong sory...
when you answer 'Panpour' to the man in Castelia City Driftveil City in dustclouds in caves you can buy it in Black City (Black Version)