Question

where is king's rock in soul silver

Answer 1

You can find it in Slowpoke's Well (B1F). Also, you can get it in the Pokelathon Dome (Mon. Thur. Sun.) for 3000 P. It's also on wild Poliwhirl, Poliwrath, Slowbro, Politoed, Slowking, and Hariyama. 1% chance.
Source
Hope This Helped :D

Answer 2

1. Buy at pokeathlone dome on MON,THURS,SUNDAY
2. Pickup pokemon lv.11-30 have 1/1000 chance of getting after a battle
3. At slowpoke well. You need strength and surf