Erm... technically you are supposed to post it in the Simple Questions post, as it is for simple questions. No matter how large it gets (and it will get larger) you should always post it in there if the question is simple enough. But I might as well answer your questions before I close this.
You cannot catch Gorebyss. Instead, you must catch a Clamperl. Clamperl can be found in any underwater area with seaweed (most commonly outside of Sootopolis City). Once you've caught a Clamperl, you need to go to the Abandoned Ship on Route 108. Navigate your way around there until you eventually find the Scanner. Now go to Slateport and find Captain Stern by the harbor. Give him the Scanner, and he'll ask you if you'd like either the Deepseatooth or the Deepseascale. Choose the latter and attach it to your Clamperl. Trade it to a friend and it will evolve. Then ask him/her to trade back.
As for Bagon, it evolves into Shelgon at Level 30, and again into Salamence at Level 50.
So... in future, please use Simple Questions. Thank you ^_^
*closes*