I did a lot of web searches and found a few places here on the west coast of Florida. I have found several places that do hydroponic gardening that also offer organic fertilizers, soil amendments, etc. so you might want to look for hydroponic places and see what they sell. What I did was search the web for places that might have the products I need. Then yesterday I spent the day visiting them to see what products they had and what their prices were. Here are some places that I found.
Simply Hydroponics and Organics. I went to their Hudson store but they have a store in Winter Park. Their website is
http://www.simplyhydro.com/Worms Way is in Tampa. Their website is
http://www.wormsway.com/default.aspxGrace's Hydro is also in Tampa. Their website is
http://www.graceshydro.com/ . This was my favorite place. Great products, prices, & staff.
I'm sure there are similar places in Orlando but it will just take some time to find them.
As far as killing weeds before laying sod you could try the vinegar weed killer. Not sure how well it works I'm just getting started and haven't tried it yet. Last year I saw a person in our neighborhood kill off their lawn/weeds by covering it with what looked like black plastic. They had it on for a long time so not sure how long it would take doing it that way.
Hope this helps in some way.