There are two places you can try...
The Candle Garden, and Sweet Decorations.
Sweet Decorations has a website here:
For The Candle Garden, if you are at the end of front street and make a left by Belize Bank it will be on your right hand side. Check in with them when you arrive to see their pricing and make sure they have the selection you want as their flowers come from off island.If you want to call ahead try this number... 206-2181 They have a short video here: https://www.youtube.com/watch?v=K_xwUWlxp48