Do you know if the ballast is in the fixture or if the bulbs are self ballasted? I'm not totally familiar with fluorescent since I never use them. But it sounds like you have a GU24 base bulb. If the bulb is ballasted, then you can just put in a bulb that's a lower wattage.
Alternatively, you can change the socket in the fixture to a standard A socket. You should be able to take the lamp to any place which does repairs and ask them to change it.

Good luck.

First confirm that you do have a fixture which takes GU-24 bulbs, then Google for dimable GU-24. I think they do exist. If they don't exist at the moment, you can be sure they will be available soon. The GU-24 base is destined to become a major standard.