My guess is they were customized by a local, high-end flooring company. That's where we would go if we wanted something similar. They can do a piece of carpet and add the band on it in whatever colors you choose.

Agree probably customized, like the pink-carpet-with-green-borders that was in our home when we purchased it ... but a lot nicer looking.

Look to me like it's just roll goods seamed together to create the band. As the previous comments mention, I would try your local carpet showroom to customize this for you. Seems like a great way to add a simple detail at a reasonable cost! Good luck!