You need:

1 Shiny Garados,
1 Pokemon G/S/C game,
1 pokemon R/B/Y game,
1 way to get a wild ditto,
and 1 game link


1. Get a Shiny Garados - G/S/C
2. Trade Garados to R/B/Y
3. Let it learn TM 31 Mimic
4. trade it back to G/S/C
5. Imporntant! delete all it's moves EXCEPT for mimic
6. trade back to R/B/Y
7. fight a wild ditto in R/B/Y
8. let it trasform into Garados
9. uses mimic to mimic Trasform
10. let garados use traform
11. let ditto again use traform
12. catch it
13. Trade the ditto to G/S/C
14. It should be shiny.

If you breed at least a shiny pokemon with a normal or shiny pokemon the chance it will be shiny are 1:64

You can also trade the shiny pokemon from G/S/C to stadium, need a transfer pack and caught 151 pokemon in G/S/C, and then trade to R/B/Y and back.