Ok if you want to gain in your arms fast, you have to do this. Train nothing but arms, do your regular arm routine but bump up the frequency to every other day. Now for the most important part: when you drink your protein shakes make sure both of your arms are raised above your head. This makes sure that all the nutrients are streamlined straight into your guns. Trust me on this, your arms will explode and you will become leaner as a whole, since you only have to provide nutrition for your arms to grow, and not your body as a whole.
edit: I almost forgot, after downing the protein shake you gotta keep your arms elevated above your head for at least an hour. Find like a sofa and lay down, prop your arms up above your head and watch television for an hour or something...