Hilditch & Key
Not that expensive for their normal stuff, and definitely not exclusive. Ask them for a catalog; if nothing else they have some good ideas on combos of colour / styles and good colour pics. As for the collar, I'm sure you could get any good tailor to make a shirt with a collar like that or make a collar like that for any shirt you have. Tailors usually have a set rate for replacing collars and cuffs on shirts and making a custom shape collar shouldn't be that big a deal. I've never seen a company offer that as an option, though the tie companies that make shirts for showing off their ties seem to offer them with higher
stance collars. For example, I have a Robert Talbott shirt with about a 1-1/2x-normal size collar. But nothing approaching this:
Of course, he also claims to sleep under ermine and sable bed coverings so I doubt he worries about getting shirts made custom.