Hi CD Bullet, welcome to the 405th. This space in the forums is actually designated for support for the site itself, rather than costume/prop specific questions, which you can ask in New Recruits or Costumes and Props.
But to answer your question: We have The Armory, with a whole heap of templates to use. The Halo 3 Recon files can be found below. It seems they are made for foam - are you looking to go the foam or pepakura route?
This is a comprehensive zip file including numerous files from multiple artists. Contents of zip-file: halo-3-mjolnir-mkvi-recon-chest.pdo Modeler: L3X BLU3R1V3R halo-3-mjolnir-mkvi-recon-helmet.pdo Modeler: Belakor Smoother: Macattack64...
www.405th.com
As for scaling, a great program is Armorsmith. It is a paid program, but makes it much easier to scale models and pep files, saving you time in the long run from accidentally making it the wrong size.