I can't vouch for them, but there are Clojure[1] and C[2] implementations you might consider.
[1] https://github.com/clojure/core.rrb-vector
[2] https://github.com/hyPiRion/c-rrb
Here’s one in Java: https://github.com/lacuna/bifurcan/blob/master/src/io/lacuna...
Here’s one in Java: https://github.com/lacuna/bifurcan/blob/master/src/io/lacuna...