you can catch it after you beat the elite four once
Moltres is in Mt Silver.
Well, lots of Pokemon on level 40-50. If you want to get Moltros, go surf to the left and go up the waterfall. Then use rockclimb on the rockpaths. When you get to the bottom, you should find moltros. Good luck catching him, he is on level 50 I think. Use ultra balls, and maybe quick balls. Hope this helped!
There's Moltros on Island one; Zapdos In the powerplant near lavander town (need surf) there's also Articuno on seaform Ilsand left entrance; you have to surf from fuchisia town.
after you beat the Pokemon league go to mount blaze [where you get moltros] you will see 2 rocket grunts and one of them will say the first part but then sees you. then go to the place where you get the Sapphire [forgot where it is] go to the end and a scientist will take it and tell you the second part then go there an get it back and to to the guy in isle 1 to give him the ruby and Sapphire then you can connect to the games ruby and Sapphire and get mewtwo in the Celedon Cave!