You can purchase via one of the two channels:Hello Sophie.
I like to buy 4 solenoids v2 thanks
http://www.ebay.com/itm/183542503790
or
https://lefongplaza.com/products/v2-replacement-vanos-solenoid-for-bmw-m5-and-m6-e60-e61-e63-e64-brand-new
Whichever way works better for you. Thanks.