I do indeed have Whites in both Bantams and Large Fowl. Nothing available at the moment since I've already culled the Whites for breeding season (which is just around the corner).
Most breeders have extra birds available in the fall. Sometimes in late spring after they are done with breeding season.
Obviously I can't speak for all Cochin breeders, but most will not sell eggs or chicks. And of course this leads to the question of "why not?" Best I can do is offer my reasoning. I do not run a hatchery. As such, I set goals for hatch numbers for each of the varieties I raise. Once I've set enough eggs to reach those goals, I do not save eggs from those birds any more. Since I AI my Cochins, this also means that I quit that process as well, which is quite labor intensive when you have several varieties in both large and bantam. So I am very eager to have hatching season over and done with. The other factor relative to shipping/selling chicks is that I also use stud matings for all my Cochins, so that I can identify both sire and dam (wing banding each chick 2 weeks after hatch), and I usually use 4 or 5 different females depending on variety, sometimes fewer. Setting eggs every other week doesn't result in a large enough group of any given color to warrant shipping chicks, and of course I am hatching a specific number to reach my personal goals. Finally, since breeders operate on a very small scale relative to a hatchery operation, they target a specific trait for improvement any given year. Providing hatching eggs or chicks from their respective breeding programs may mean they are sending that one bird that has the desired outcome of that year's breeding goals to someone else.
I agree with NYREDS. Learning your respective breed via the Standard of Perfection and visiting shows/talking to breeders in your area is the best way to learn about exhibition poultry. Even if you never intend to show, it doesn't cost any more to feed a bird that conforms to the standard than it does one that lacks breed characteristics.
Just my 2 cents.