assuming one kept there mouth shut and was discrete no one would know , however if your the type that would even mention it on a forum before getting one ,then you are not one to keep there mouth shut if you did "find" one.
the worse that could happen is you get some time (any amount of time) inside , and while inside lets just say you end up with a hole as big as a snakeheads mouth , iam assuming this may be carried out by someone calling themselves mr. big. that's probably the worst but hey they may do nothing , so give it a go . its only a little hole that you are gambling with.
The question you should be asking if you really want one type of fish bad enough is "how do I change the law" .
ill be honest with you all , we in the uk are not allowed pitbulls or fila brasilianos both are dogs that many now want just because there banned. its just all hype folks , if any of them got either dog they would be board in a week of them . just like if you guys got snakeheads you would be board in no time at all . there are plenty of legal species that are just as good as channa , there are many species that are as good to breed like bettas and many species that hit food as hard like pbass or wolfs there are certainly better looking fish out there , better tasteing fish out there , rarer fish out there , more expensive fish out there. don't get me wrong channa are my fish of choice but if they where to be banned tomorrow then I would be happy to find something else to keep .