The "bust" pictures? Hand grenades and RPGs are sold at gun shows all over the country. They could be sold by private sellers who may or may not require background checks.
Here is her proof that hand grenades are sold all over the country at gun shows. Unsurprisingly, none of her links said anything about gun shows:
more about hand grenades: http://yarchive.net/gun/politics/hand_grenade_bank_rob.html
I guess this one is for a "practical joke": http://mp-pistol.com/boards/lofiversion/index.php?t20494.html
and this one: http://badphoenixcops.blogspot.com/2009/11/for-sale-60-hand-grenades-200-each-will.html
Apparently, P.T. Barnum was right. The first link is to the type of baseless, unsubstantiated story that makes up most of the gun control movement's "facts". The second link is an anonymous classified ad (because none has ever submitted a fake classified ad). The third link is a demilled grenade which you can buy at any government auction or military surplus store.
And the final link flies completely in the face of the notion that American gun shows are arming Mexican criminals as it's an example of the complete opposite. Apparently, it's Mexican criminals that are attempting to sell their grenades here in the US.
Common sense and critical thinking skills go hand in hand. One cannot exist without the other. It's apparent that Joan Peterson possess neither, otherwise she would do more than post random Google results as her proof that hand grenades are being sold at American gun shows.