Quite simply Ecudorian roses are the biggest you can buy and absolutely stunning. The Dutch simply can't afford to grow them to the same size because they would need tons of heating/light etc which obviously is far more expensive in Europe.

A large percentage of the Ecuadorian production goes to Russia and Japan where they pay way over the odds for the grade, length and head size but you can get them over here ... allbeit more expensive.

Alternatively look at Colombian roses. Not quite so big be equally fab and very long lasting. I'm due to visit some rose farms in Colombia in July ... will report back.
C