Happy Inventing!
It is not a requirement to have a patent to show your invention to anyone ever in the US. However, it is a good business practice to have a US patent, assuming it is patentable as Mr. Neustel mentions in his post, if you are selling into the US. It could help prevent competitors from knocking it off.
If you can not get a US patent, you can still show it and say it has patent protection without telling anyone where

You could also have a closed booth and only invite buyers in to see it. This is common practice with the large distributors. It is just more difficult to get the buyers in when they don't already know who you are. Try setting appointments with them before the show. Do good marketing and that could be just the ticket!
Hope that helps.
Lisa