Not 100% sure but seem to remember that the Dutch season starts around end of June, you could best check that with your/a Dutch supplier.
My other thought is, and not knowing the US market much at all, but does their season start earlier the further south you go in your country, could you check with suppliers/FC members in more Southern States?
(reason I say that, our hydrangea season just finished about 5 weeks ago, low and behold: they just peaked and are still going on the south island and we just got the most beautiful heads in, different latitudes and growth peak times, could be the same there?)
My next suggestion would be to take a second choice for flowers just in case, best of luck