A:Answer You can buy the extensions individually in a number of places, including BestBuy - look up "Philips Hue LightStrip Plus Extension". However, they are getting harder to come by because these older ones are being phased out in favor of the new Bluetooth strips. Be aware that you can't chain the new Bluetooth strips to the non-bluetooth Lightstrip Plus.
Also, be aware that every time you add another extension, you'll lose a bit of brightness, since you're powering more lights with the same amount of power.