Pixhawk Radio Telemetry Suggestions

Can anyone suggest me a Radio Telemetry Pair for covering at least 50 Km with Pixhawk 2.1?

At present, I have 433MHz 500mW 3DR Telemetry. Can I increase the antenna gain to increase the range?
This is for Mapping purpose and 900MHz is illegal to use in my place.

It’ll be very helpful if someone can suggest me a solution for this.

Before going for Satellite communication or MAVLink-MAVroute-Gstreamer, I would like to know the possibilities of increasing the range of communication with 433MHz itself.

Thanks in Advance.