I couldn't find this anywhere so I spent the night drawing up this template from two screen caps as well as some help from SITHcamaro's build (which has been posted somewhere on here). It's 36 inches from tip to tip, which seemed right based on the aforementioned reference images and also me holding a 3' piece of pvc pipe and pretending to shoot at Nick Fury's helicopter.
Loki Spear Template.png by zlindee, on Flickr
Each color was created as an individual layer in photoshop so I can turn each layer on and off. I wish I could upload the .psd because it infinitely increases the file's usability in my opinion.
I plan on starting this build sometime this weekend, if I do, I suppose I'll use this thread to post updates.