Also don't forget BMWCCA members get fair discounts (up to 20%) at some dealers. You'll need to check around.
They won't have what Mesa or La Jolla Independent have in stock and they probably won't be able to spell "E9" if you spot them the "E", but if you know exactly what you want, then they are an option.
If you want decades and decades of experience, friendly advice on alternatives and access to slightly used items that may be otherwise NLA, then our friends at La Jolla Independent and Mesa are a highly recommended source.