it's modeled from a real Knife, yes. That are custom made. Sorry I do no remember any of the details but I am 100% positive it's from a real nice because they had pictures of the acutal knife when it was first added to CS.
I looked at csbanana, and there they call it the "bowie knive", but i searched google and i can't find it, but like with all the weapons in cs maybe they just made it a little different than the real knife so they wouldn't have to pay licensing fee to the makers.