Honestly, I'd recommend turning on the game, finding a sparrow you like, and turning at a good enough angle to see most of the details of the front, top and side. Only hard part would be the back (you could fib it with enough dedication). After that, screenshot it and upload it to your computer. From there, you can try to find official sparrow measurements, use pixel measurements of you picture, and math proportions for everything else. This is what I did when I had the same project.