The school bus company does not run the route to Shatin/Tai Wai. But there are two nanny bus companies run from Ma On Shan--> Shatin--> Tai Wai. I think the time for getting on the nanny bus is around 7:00A.M.
My daughter takes a nanny bus and she tells me one of the stop is 瑞峰花園. You can call Mrs.Lai for more details.
( I don't have another bus company's information)