There are three god capes that you can get: Saradomin, Zamorak, and Guthix, which all have the same stat bonus.
To get there, take to an Oracle of Dawn. Click teleports>others>mages bank. Use the pool directly north, and then run north.
Pray to whatever god you want your cape from and it will appear on the ground below you for free.
You can also buy it from oracle>shops>magic armor.
Staves can also be purchased from the chamber's guardian store for 80,000 coins. He is found in the same cave as the statues.
Capes of any sort will all give +10 to magic bonus.