Click on the Maplin website. click here
Look for the search box in the right hand corner of the web page and enter "cooling fans". See if any of the dimensions resemble that of the laptop fan.
Remember though the voltage will also have to match.
Also remember, a new fan will not remedy any damage already caused to your laptop.
Before any of the preceeding, get a can of freezer spray sold by Maplin and spray it about 20cm from the area the fan was protecting. Boot up the laptop and see if it works. Keep regularly spraying through the experiment.
This method is a bit rough and ready but is regularly used in the electronics industry, to check for faulty overheated components.