Just get a generic charger from EBay. They may be available elsewhere. Get a 12 volt 500-600 milliamp one or if you know the exact milliamps for your charger, use that number. Here's a link to one on EBay.

http://cgi.ebay.com/12-VOLT-AC-POWER-SUPPLY-ADAPTER-12V-DC-600MA-CHARGER_W0QQitemZ300404845865QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item45f1862d29

I'm not recommending this particular one, just using it as an example. Good luck!