I wanted to suprise people with this in game but i guess this is as good time as any.
The way that I will do the other starters, Everglade region is home to every starter pokemon except G/S/C ones, they are trying to be bred into the region by importing them from johto.
The pokemon trainers receieve from the Professors all orginate from the Everglade region, they are specially bred, and raised from eggs until level 5 where they are transported to the region which needs them.
You visit this pokemon breeding farm on a certain storyline event, in which you can decide to steal one of the pokemon or complete a series of missions based at the farm, one which includes visiting the parent pokémon to recieve egss of the previous starters. you will not be able to get all of them at once, so it is once again based on your reputation.
If you decide to steal it, it will bring in another new feature that I am implementing, the usage of reputation, but this time it has a purpose, after graduating the Pokemon Guild, you will be told that your rep will effect the amount of guild missions available to you, while you can increase rep easily, by completing missions, you can also lose it easily, but doing bad things, or by not fullfilling certain critearia set by the person in need.