The rare golden relics are only found by luck - I think I collected three of them while I was completing my JA collections. She did have full archaeology skill and had completed both the JA aspirations, but I think that only gives a Sim a slightly better chance at finding rare things.
I'm fairly sure I found them in the temple treasure chests, but that's the only direction I can give. Once I'd found all the plates and assembled all the possible relics (which took a few Sim weeks), I was ready for my Sim to move on with her life, so I gave up on collecting the rest of the golden relics. Maybe one of her decendents will fill in the gaps.
The death relic can be activated multiple times. I can't remember if it has a cooling-off period, but it can definitely be used again. The danger with the wooden relics is that they can occasionally break while being used. The golden relics don't break.
