The jar or the zip?
If Jar
No, you don't need it. Even if you had it you wouldn't be able to do anything with it. Simmy's code is such a mess that figuring it out would take a lifetime
If Zip
You want to make a texture pack. That's all fine and dandy but if you don't even know where to find the file then you're going to have a hard time
Either way, it's stupidly easy to find the files you're looking for. The fact that you've made a thread asking for the file that you already have access to makes me doubt you'll actually be able to do anything with it to begin with.
Bonus points
If you're talking about the source code: HA