Dolgat in Gold, Silver, and Crystal

 Dolgat is much easier to catch in Gold and Silver than it is to catch in Red, Blue, and Yellow. All you have to do is go to the Lapras Cave on Thursday and fish. A Goldeen may appear, but don't be fooled. It is actually a Dolgat. The game will not let you rename a non-Dolgat Pokemon to Dolgat, so if it lets you, then it is a true Dolgat.