Commons RNG is focused on pure-Java implementations of standard deterministic generators.
Quite a few algorithms could be added, but priority is on fast generators that generate sequences of pseudo-random numbers; i.e. the requirement is strong uniformity, but not strong unpredictability (a.k.a. true random numbers).
In particular, in Commons RNG, there is no provision for using an external entropy pool.
Beware that some well-known (and much used) algorithms have been proven to fail spectacularly on the uniformity requirement.
Would-be contributors should look at the commons-rng-core module for how to implement a generator, and at the commons-rng-examples module for how to test the uniformity requirement.