I wasn't online for a while but "later is better than never". (translated from the French) Here's a few flower shops with e-mails so It'll be easier to contact them.
Amaryllis Fleurs
150 Ave. John Brown, Lalue, Port-au-Prince
Phone: 34 01 33 04/ 37 70 93 25
Email: amaryllisfleurs@yahoo.com
Formes & Couleurs
74 Rue Grégoire, Pétion-Ville
Phone: 34 58 06 06/ 22 57 02 28
Email: mcvcraan@gmail.com
Source: PagesProHaiti.com (a business directory)