jDrones and RFDesign offer long-range SiK-compatible telemetry radios. The radios provide reliable connectivity at greater than 5km ranges with normal antennas (and have been reported to achieve much greater ranges).
jDrones have productized RFDesign modems (added a casing with power management, filtering and other electronics inside, along with cables to connect to popular flight controllers, and individually validated antennas). The first such modem was the RFD900, but both RFDesign and jDrones have since iterated to new versions.
The jDrones radios have a JST-GH connector, and come with cables for: JST-GH to JST-GH and JST-GH to DF-13. They can therefore be used in a "plug-n-play" way with most Pixhawk Series controllers (you might have to change/use an appropriate connector for some "non-standard" boards).
There are a number of versions available: