Despite Abit not making the fans anymore there are various other 3rd party options available (have a look
here for various examples depending on what you need).
If you have decent air circulation inside your case you could most likely do away with a fan altogether and replace it with a dedicated heatsink, your local shop should be able to fit one for you.
...Or if worst comes to the worst, to try and give your existing fan a bit more life, you could try and clean the fan fins with something like a toothbrush yourself. Dust gets clogged onto the fins that wont be removed by a simple case hoovering but it's a fiddly job and may well be for nothing if the fan has been permanently damaged.
Iain.