You can get carbon fiber enhanced PLA, but you get short fibers. [Stefan] glued long pieces of carbon fiber exactly where he wanted them using epoxy. This method did provide some benefits.

Since I started 3D printing, I’ve tried out a bunch of different filaments in my projects, from basic PLA to nylon blends ... When people talk about carbon fiber’s strength in industrial ...

While the claimed benefits of carbon fiber filament sound ... is a top pick for strength and heat resistance. It can handle everyday stress better than PLA, making it great for prototypes ...

[Thomas Sanladerer] wanted to make 3D prints using carbon fiber and was surprised that it was fairly inexpensive and worked well, although he mentions that the process is a bit intense. You can ...