12/2 and 14/2 has a ground wire. When you're counting wires you don't count the ground so the /2 is going to be standard 3-wire residential wire. I just bought 50' of 12/2 at Lowe's for about $30 and the 14/2 was about $20. I can tell you that most electricians don't consider that amount as scrap and most also recycle their scraps with the prices of copper so I doubt you're going to find anyone with that much 'scrap' to give you. You can get a 3-gang box to wire up but do you need all your outlets at the same location? Unless you have a special need it's usually better to do more single gangs spread out in various locations in case your needs change. It's super easy to just get something like this to make more outlets at one location and take out when not needed (or better yet add something with surge protection):