Central Florida has many racing venues. Space Coast Sod Slingers in Melbourne (and soon Sharpes), races held monthly. Florida Lawn Racing in Avon Park, races monthly. Grasscar in Fort Myers and Labelle race several times monthly. All are on the internet with web sites most can be found on FaceBook too. Of course you can always contact the USLMRA or ARMA to get contact info for local clubs too. As far as pulling clubs for lawn tractors the only one I know of for sure is at Florida Flywheelers Park near Avon Park, they have a website too.
The Space Coast Sod Slingers is a USLMRA Affiliated club running US Open rules. We prefer any NEW builds to be USLMRA legal, but we'll accept any safely built machine.
I would love the contact information of the group you found that races 4 times a year. I am trying to get the names and numbers of EVERY racing lawn mower owner in the state. Whether they are active of not.