In the 3 series accessory brochure the tips are listed on page 19 different part numbers for E90/E91 and E92/93 priced at 29.95 each. The E92/93 are different lengths to give the staggered look.
I normally get 10% off these prices for BMW car club membership.
Look at TStevie - bits for sale in UK classifieds. He has a set of tips for sale