For perspective: There are also the expressions
～ろうと～ろうと
～ろうが～ろうが
e.g.
よかろうと悪かろうと be it good or bad
早かろうが遅かろうが be it early or late
I think these expressions are more productive than ～かれ～かれ, although they do have an archaic feel to them.
Also, it might be interesting to know that よかれ is commonly used in the sense "good intentions" or something like that:
よかれと(思って)したことが裏目に出た I did it with good intentions but it backfired on me
～かろう, although slightly archaic, is still sometimes used instead of ～いだろう
それはおかしかろう！ (You have to admit) that's strange!
