How do you farm guardian parts easily?

How do I get giant ancient cores easily? I really need guardian parts, especially giant ancient cores to upgrade my ancient armor. I followed quite a few tutorials, but they all are either, have the guardians, but don't drop like it was in the tutorial, or there is no guardians. I tried ancient core duping, but it took forever, but it didn't yield any giant ones.

Solution 1:

At Hyrule Castle, if you have a good look-out and some ancient arrows they should be easy to eliminate. You'll find them at every corner. If you're not ready there's a few by the bomb shrine on the great plateau and a handful in Hyrule Field on the north side nearest to Hyrule Castle (you don't have to go close to it).

Edit: Oh! I just realized your question. The stationary guardians at Hyrule Castle (guarding that tower upward, which shoot multiple times when detecting you) have a chance they'll drop giant ancient cores. I got one once.