You will not likely find an DIY earth loop kit.
The pipe is warranted for 50 years when done by Certified Trained Installer.
The pipe joints are all to be done by Heat Fusion process which requires a set of special fusion tools and proper training.
On a side note, this Fusion Technology is the same as what is used for the Natural Gas Utilities' buried plastic pipe.
What is your constant ground temperature at your latitude?
It's 54* F here at my location.
I have 15 years been running water to air heat-pump that I self installed in 1995. It is an open loop system w/ well water. Some would call it "Pump and Dump"
Everything original as from day one. I do have a second submersible well pump and swap the two...good cleaning on one coming out and it's ready and waiting for next time.
I also bought a used Geo for cheap and installed it for my "Man Cave" over top my detached garage...used same well and same drain field...twice as nice.
BTW...My system paid for it's self a long time ago.