There is a vehicle bulb replacement guide on osram.com, and yeah, it's a H4 unit 55/60W.
These are available from about $2/each in every single shop here up to about $20 for premium
units. Bare in mind that the 50-90% higher output bulbs usually have a shorter lifespan and
some manufacturers (like Philips) have specific motorcycle bulbs designed for better visibility
of the vehicle (has an orange glow but casts pure white light) and longer life of the bulb in
motorcycles (a lot more vibrations then in a car).
Don't buy anything with a bigger power rating as you might melt the reflector or plastic cover.