You can get it on ebay, this is the one I buy:
http://cgi.ebay.co.uk/5-L-Panel-Wipe...item5195e7be62
5 Litres might be more than you need, but its handy stuff to have.
Could check your yellow pages for a local paint supplier.
Halfords do sell aersol cans of 'Surface Cleaner' which is the same thing:
http://www.halfords.com/webapp/wcs/s...Id_165594#dtab