Truth be told, the G36's single biggest impediment to accuracy is its atrocious, gritty 12-lb Trigger-press. If you purchase one and wish to wring out the inherent accuracy of your HK or Walther Barrel, you will require one of two things - either an SL-8 Trigger Group, or a Tommy-Built G36 AR15 Trigger Group Housing. The former gives you a much lighter and smoother Trigger-press than the inexcusable stock G36 Trigger, akin to a "Match" version. The polymer AR15 Trigger Group Housing is exactly what it sounds like and gives you the ability to run any after-market Match AR Trigger Group in your G36.
I obtained the G36 Trigger Housing for AR15 Trigger Groups through a 3rd-Party Importer back when I had my rifle. I ran a Trigger Tech curved AR Match Trigger Group with terrific success once I solved a minor fitment issue. I had to grind away an inconsequential portion of the aluminun "Cassette" that holds the Trigger Group together in order to get the Trigger Pins aligned.