Iraggi alts can be found on Ebay or Excessive amperage.There's also Ohio Generators but I hear a lot of bad things about them.There's lots of options depending on what kind of car you have.
I've heard tons of bad stories about Ohio Gen though...I've never run one personally but I a couple guys from CA.com said they put Ohio Gen alts up against Iraggi alts rated for the same amperage and the Iraggi alts absolutely destroyed the Ohin gen alts.