Wow, you know the brand name and you can't find where to buy? Lots of online places and I would expect just about any bike shop.
The brand specific models vary only in how the sensor mounts and the magnet, the actual display unit is the same. If you can't find a brand/model specific unit you can buy a generic model which will have a magnet that you will have to glue to the wheel. The brand specific models will usually come with a small bolt that has a magnetic head. The bolt replaces one of the bolts that hold the brake rotor on.
Trail Tech has several models and most are battery operated so they don't need any electrical connection to the bike. I am not sure but I believe the ones that do have electrical connections are just for a light so that you can see the display on night rides. The internal battery is one of these little coin cell batteries and they will last a year or more.
Rod