Welcome to Fierceboard! Make sure to read around the forum a bit before you post too much- most people on here are lovely but some people can get a little irritable sometimes!
As for your question, I'm sure it's true of the US as it is of the UK, almost all allstar programs will take athletes who have no cheer experience at all. Placements are around now in the US for allstar teams, so if you want to be on a team for the coming season you may have to start looking soon!
Otherwise, lots of allstar gyms have tumbling classes which you can attend which don't require you to have any practice but will coach you in tumbling.
If you look on the "wiki" section of Fierceboard there is a list of gyms by state which will help you find some if you don't know of many in your area; equally a quick internet search should turn some up.
Good luck with whatever you decide to do, allstar cheerleading is great fun! :)
