Unlikely you can find peonies in August. Only sources would be Alaska, Canada, or the southern hemisphere. Mano Capano, of Pivoines Capano does cut peonies in Canada. She might have them. The peonies would need to be cut and held in cool storage until the wedding and then the problem would be getting them to Mexico.

You could of course give her an artifical bloom and a gift certificate to one of the growers. Thus giving her a gift to grow with your marriage.

Here is a link that might be useful: Mano Capano

Hi Chad. My name is Keri and I was in the same predicament a year ago that your fiancee is in now. I wanted peonies SO BAD for my Aug. 11th wedding and it took me forever to find them. We ordered our flowers online and made the bouquets ourselves. Look on fiftyflowers.com, http://www.fiftyflowers.com/flowers/AllFlowersPeonies_57.htm
They will ship peonies in Aug. as long as they have them in stock. I ordered the Sarah Bernhardt peonies for my wedding, and even though they were the priciest out of all the different flowers I ordered, they stool the show in my bouquet. I'm not sure if they will deliver in Mexico but it's worth a shot calling them and finding out. I found their customer service to be very helpful, as a bit of a bride-zilla I was paranoid that they wouldn't arrive so I called quite often to double check the delivery address they had. : ) Well I hope that this info was handy and that your wedding flowers turn out beautiful.-Keri

You may try Bagoys florist 907.227.1922, Petals and stems florist 907.561.7774, the Peony lady of anchorage (Judy Wilmarth) or Carrs Florist all of Alaska 907.339.1270. Alaska Hardy Nursery 907.235.4969 Good luck!