Is it still possible to get shiny starters? If so, what is the probability? And Beldun shiny it's possible?
I believe the probability is about 1/4000 or so, and yes, Beldum shiny it is possible
Yes, and you dont really have to stress about soft-resetting since you can catch and shiny hunt them in the wild.
Mudkip is in the first area ( around the spawn next to the bridge ), Treeko is in the second area, and Torchic is in the final area.