Well what you are looking for are mostly in the Ocala National Forest. Alexander, Juniper and Salt Springs all federal parks. There some other possibilities: Rainbow Springs on the Rainbow River SP and Silver Springs SP on the Silver River. Most of the other state park springs have short runs or don't have campgrounds. Ichetucknee Springs SP has a fantastic run on the river but no campground but there are private cg nearby.
All of these parks have private cg nearby. All of these parks are about an hour or hour and a half from Orlando. There are other parks scattered further south but that is the main grouping.
Now I'm sure you are aware that these places are probably booked solid for the snowbird season. But I'm seeing reports that the lack of Canadians is opening spots since they cannot easily escape Canada right now. So that may open some spots.
I saw a report in the RV News that said Canadians are flying to Seattle and paying to have their RV's trucked across the border on flatbed semis. That works since the US isn't hunting them down and issuing $10,000 fines like Canada is doing. But that is just a trickle compared to the usual flood.