Just buy the complete top case for the iBook 1.2ghz on ebay. Not very expensive. It will be easier to find than just searching for the trackpad cable or check with sellers that list many iBook G4 parts and contact them via ebay to ask for the trackpad cable. One member here, rdklinc, has many iBook parts. Maybe he can help you. You can send him a email thru ebay, check here:
http://myworld.ebay.com/rdklinc/