What kind of guns do they sell in gun shows?

"Semi auto, SMG, and assault rifles" ARE rifles, period, the word assault rifle doesn't necessarily mean it is full auto. The seller would need to have their class 3 FFL and the buyer would need to have a class 3 firearms license in order to buy something full auto. All of the above can be sold at a gun show, including the MP5K that you want, depending on if someone there has them and is trying to sell them.