how do i get it

HI,

If you have Mountain Lion you don't (you have Messages)

iChat comes with the OS in any version back to iChat 3 (earlier than that it was a Download.)

Version prior to iChat 6 in Lion can be "reinstalled" using the Install DVDs

Lion needs to be Reinstalled to get iChat 6 "back".

Other than that I am going to be guessing what OS you have.

10:11 PM Saturday; December 29, 2012

Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"

 iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.2)
 G4/1GhzDual MDD (Leopard 10.5.8)
 MacBookPro 2Gb (Snow Leopard 10.6.8)
 Mac OS X (10.6.8),
 Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images."  No, Seriously