Swift 4.2 Alternative Random Number Generators (RNGs)

I'd like to implement i) a seeded RNG and ii) a seeded RNG with a [Normal] distribution, as alternatives to the new SystemRandomNumberGenerator implementation in Swift 4.2, so that I can then use these RNGs within the newly introduced random methods.

My preference would be to do it this way as 4.2 intends, rather than via gameplay kit.

Does anyone know how to do this please or any open source projects doing it? Thx