Basically, you can't.
I asked the self same question in 2003. It has something to do with the frequencies. The frequncies which our walkie talkies use are not available for the public to use in the US. It's possible that they are restricted to the emergency services or the military. US bought walkie talkies use a different frequency range. They can't be used in the UK. Catch 22,
Not sure that anyone would swoop down and arrest you or anything but I guess the regulations are there for a reason.
When you get to FLorida, buy there but don't be tempted to buy ones which are cheap versions as there's too much interference and you can't hear what's being said. Ours were $50 from
Walmart. Work fine. Our friends bought some for $30 from the Radio Shack and they didn't work except in the villa and it's estate]