Difficult one - you can never be certain whether plants will flower a month early or a month late. There are some annuals you could grow specially, though you'd need a fair bit of ground space to produce enough for flowers for, say, tables, etc, such as Clarkia, Gypsophilia, Calendula, Cosmos, Molucella, Nigella. Lilies might or might not be in flower at the time, they're usually a bit later in July.

do you have a friend with a greenhouse who could grow them on for you? but as Bamboo says its difficult tho guarantee anything

Thank you- I'm hoping to track down someone with greenhouse space to make sure we have something at least. Really like all your suggestions, Bamboo, but particularly Clarkia and Calendula. I'm hoping that if we send out enough variety of seeds we'll have something in bloom around the time of the wedding. Cross fingers...! Thank you both of you for your help.

Irises might be a possibility

Clarkia definitely will be...