Hi, Dom! It's a really safe bet to buy directly from the manufacturer. You'll be safer when it comes to getting a warranty. Amazon.com sells these batteries, but they're sold third-party, so you may not get a full warranty.
Here is Dell's Inspiron Mini 1210 tag search page:
http://accessories.us.dell.com/sna/PfydFeaturedCategoryResults.aspx?c=us&l=en&s=bsd&cs=04&mfgpid=199994