You can go to your nearest vinyl/sign store, perhaps Fast Sign, and purchase as much vinyl of any color you want. It usually comes in rolls of 30 feet or more. It is usually 13-14" wide, which is not that efficient if you want to duplicate the factory's standard 8" wide stripe. Applying them yourself requires lots of patience, but it is doable. I've done it several times on my car.
If you want a really professional job, contact Al Roberts, a member of the Southern California VCA. I don't know his phone number, but you can contact the club at their web site and get it.
He's in the business and can make you pre-cut vinyl stripes that will fit perfectly. He'd also be happy to install them.