This whole idea of "Nazi memorabilia" at gun shows is being overblown by the antigunners, to make gun owners look bad. In my experience, the trade in WW2 memorabilia (including Nazi stuff) is driven by historians, collectors, and reenactors, not by neo-Nazis. And remember, most of the "Nazi memorabilia" was originally brought back by American GIs, as souvenirs. Those were the last people who would extol that ideology.
Nevertheless, we need to recognize that sensibilities have changed over time. The vendors need to be discreet in their display of such items.