Any standard auto parts 55/60 H4 halogen (9003) will fit, once the tabs are cut off.
Many order off road 80/100 9003s for only a little more, and the brightness is greatly improved day and night, properly aimed headlights do not get flashed at night on dims (80W), and they have been run for years with no heat issues in the fairing, bulb socket or wiring (the IS fairing breathes/is vented very well.... these cannot be used in the std/tourer bucket).
Read the reviews, some are better than others (ie bad write-ups on the Hella Optilux)
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=80%2F100+H4+bulbs&x=11&y=17I could never find them in stock at auto parts counters.