Ok so besides the obvious lie that your title suggests, and now that my heart stopped beating so fast, here's what you're looking for...
I did a google search for WETA ODST combat knife, and the first link that popped up was this...
Halo 3 WETA ODST Knife
The first reponse the guy had was this...
"Easy.... Kershaw's Responder........ hope it helps"
Also here's a link to a sales page, but you can look around for better deals I'm sure.
Knifeworks - Kershaw Responder
-Magnum