Yes, all five of my current roosters are not human aggressive, and all of them would also die to protect the flock from a predator. They don't view me as a threat - or as a challenge to their flock leadership because they know I'm not a chicken. Your rooster either views you as a threat to the flock or as another rooster trying to take his flock from him that he needs to fight because he thinks he's dominant. I had an aggressive rooster once, the only rooster I haven't raised by myself; he showed up one day during the early days of my flock, and no amount of picking him up, chasing him, pinning him down etc would break him of his aggressiveness. I'd pick him up, hold him for a bit, put him back down, and he'd be right back for round two.
Your hens should adjust well to a new rooster, if it turns out to be necessary. If you get a young cockerel they'll probably push him around a bit before he learns to take charge, but if you can find a nice older rooster he should take charge right away with few problems. He and the more dominant hens might have a few quick scuffles to settle things, but that should be it.
To find a new rooster, just check your local craigslist. You'll find tons of them looking for new homes. Make sure you quarantine any new bird for at least two weeks though so you don't accidentally introduce a nasty disease like MG to your flock.
