Copper Kits
I've sold a couple of thousand copper slimlines and have had no complaints about them vis-a-vis wear and/or tarnish, I think most of the rumor is just bulls___, silver which also will tarnish, is also a soft metal has been around for years and I've never had any complaints about that either. I have two year old pens with the finish on the copper parts as bright as when it came out of the package. And, I suspect you should be able to find copper with the clear epoxy coating that will last a long long time.
Best Regards