Yes a comprehensive calendar can be hard to come by but it's not for a lack of trying. Rick has a schedule that he maintains on this site but the schedule is only as good as the information provided. Below are two very well attended F18 events that were pulled directly from the schedule on this site:
Jan 13-15 -- Tradewinds Midwinter Open Cat Nationals/NAMSA NAs, 3-days of racing (even if you can only make Sat/Sun, you will get scored your average for Friday). This is the biggest event of the winter. Carlton Tucker Memorial Award to Winner of the Largest Class, Also, F18 Midwinters, F16 Midwinters, Shark Midwinters, Wave National Series Regatta, Harken Buoy Series (1st for 2010 and Awards for 2009), firstname.lastname@example.org, 305-451-3287, For PreRegistration: http://www.catsailor.com/registration/
Here is the Notice of Race Info: http://www.catsailor.com/Tradewinds.html
Feb 2-5 -- 3rd Annual Charlotte Harbor Regatta, Expected Classes: Wave, F16, F18, H16, Weta, & Windrider. www.charlotteharborregatta.com
For club races you can try Gulfport Yacht Club, they race the first and third weekend of the month.http://www.gulfportyachtclub.com/
You probably won't find info on the Macho Man, it's not that kind of regatta. The Macho Man is strictly run what you brung, no OA, line honors event where second place is just the first loser. It's a bit of a longish distance race (65 miles) for most weekend racers so it's typically lightly attended when it happens. TBCS tries to organize it but it's really just up to the group of the willing if and when it happens. If you want it to happen Mr. "we do better in the monohull fleet" start talking some trash and I'm sure you'll spark the interest those anxious to stick it to a monohuller. Yes, we can be just as bigoted about our rides as those in the monohull fleet.
As for the Miami Key Largo regatta, that one is almost always a secret.
Welcome to the multihull fleet, <some derogatory remark towards monohulls here>