I would just use a straight, plane-old henna.
I use the Henna Guys and love it, but mine has Hibiscus mixed in, so it comes out more of a true, vibrant red.
Your hair is darker than mine, so you don't want any darkening agents (indigo). You say you want coppery ends; plain henna is a red-orange (different sources of henna lean toward different ends of the red-orange spectrum). Henna hut is a good source for henna and henna for hair has a lot of good information. I don't buy at henna hut, but only because I was so happy with what I got from the henna guys, I didn't see any need to buy anywhere else!
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