Sorry, I don't think they've come up with a way to STOP grey hair from growing. Only ways to cover it up. And they do grow in bunches sometimes. Listen, I love every grey hair in my head and I have long blonde hair that is all different natural blonde tones. I don't have many yet but each grey hair is a badge to me. A medal of sorts. I earned that grey hair and I wear mine proudly. It's inevitable. There's great stuff out there for coverage. Don't panic! There is nothing WRONG happening here!
About a week ago, my girlfriends and I were watching an episode of The Walton's. (Please don't say "yuk!". For some reason, we hated it, now we like it!) And there is a character on it called Cora Beth. She has jet black hair and a streak of grey that runs from her forehead to the back. When we saw this we all went "Wow! How do you get that!" and my best friend, Nina, said, "I can't wait for my greys to come in." Relax and think of how beautiful you are.