From one newbie hobbiest to another (I've only been at this for 2 years now), the only thing I can say confidently is that you will find it VERY difficult to find good Silver Grey Dorkings to work with. My first flock (aka my "practice flock") was comprised of hatchery birds purchased from local feed stores of a few breeds I was interesting in. After raising them for a few months I decided that the SGD was THE breed I really wanted to work with. I still haven't been able to get my hands on any, and finally decided to switch my focus to birds that fit both my climate and my objectives better. So....take you time, don't be afraid to experiment, and be both patient and diligent in your endeavors. This is the one hobby that allows for you to eat your mistakes and start over, so you're never at a complete loss, and you learn from every project. And most importantly...HAVE FUN!!!
Good luck!