I don't think the flea market is the problem. Except for maybe Moon, your birds were lost to accidents not to illnesses. I don't know what happened with Moon, but you can keep an eye on the remaining birds to make sure they all look healthy. You can check the aviary for potential problems, for example: potentially toxic plant material falling into the aviary, wild bird droppings falling into the aviary, insect infestations, birds chewing on the wires for entertainment. Mosquitoes are obviously a huge problem in Florida and they can carry West Nile virus, but there are things you can do to reduce the problem. Here's a link:
http://www.birdsnways.com/wisdom/ww69eii.htmGreen vegetables are definitely good for them and it's best to provide them. Birds can be picky about the presentation, and my guys don't like cut-up vegetables in a bowl unless it's corn kernels. But they love leafy greens clipped to the side of the cage and broccoli florets.
If you got any new birds you would need to quarantine them, but you don't need to quarantine your current birds from each other. If Moon had a contagious illness they've already been exposed to it. The exception is the babies who have been in the house with you. Wait at least a couple more weeks before you put them in the aviary to make sure the other birds are healthy.