You have to make your own and add it
You can do it like this (this is for a custom button using an image)
UIImage* image3 = [UIImage imageNamed:@"favorites.png"];
CGRect frameimg = CGRectMake(0, 0, image3.size.width, image3.size.height);
UIButton *someButton2 = [[UIButton alloc] initWithFrame:frameimg];
[someButton2 setBackgroundImage:image3 forState:UIControlStateNormal];
[someButton2 addTarget:self action:@selector(loadFavorites)
forControlEvents:UIControlEventTouchUpInside];
[someButton2 setShowsTouchWhenHighlighted:YES];
UIBarButtonItem *favoritesButton =[[UIBarButtonItem alloc] initWithCustomView:someButton2];
self.navigationItem.rightBarButtonItems =[NSArray arrayWithObjects:favoritesButton, nil];