Srijan, take a look at the link ploffer sent.
In his picture, you can see the Cameron Sino logo (CS) in the bottom left corner of the battery.
Those are the ones to look for.
Of course you can grab any ebay battery marketed for Iriver hxx0, the polarity should be fine. But anecdotal evidence tells that performance is inferior, and some batteries suffer from swelling.
The first major Ebay seller who supplied the CS was Lickety Split Auctions:
http://www.licketysplit.ca/He doesn't have any batteries out now (away for Christmas?), but drop him a line and ask for a deal off-ebay.