Remember not all Nazi collectors do it in support Nazism. I had a neighbor growing up who had a book shelf with many Nazi items. She and her husband were both WWII vets. She used it as a conversation starter to speak of the evils of the Nazis.
Look at it this way: They lost...now we get to sell their stuff
On a more serious note, some people like to add more to collections that just guns. A person might start out with a K98, and then want to add the uniform, medals and propaganda posters to go with it. They might take a Garand or an Enfield and do the same thing. Its all part of the history aspect, but sometimes getting rhe read deal can be a little costly. I don't think the stuff is there to Idolize Hitler or the Nazis, any more than a bunch of old Soviet stuff is idolizing Communism. Its just "stuff"
I live in Ma, some shows have it some dont. depends on the show and who pays for a table.
I guess I am not paying attention to that kinda of stuff in NW Fla. I don't recall seeing any. I have been 3 or 4 times when the show comes to town and I have always been more interested in guns and holsters so it might be there but I didn't notice.
I got to the show (Suncoast Gun Shows) every time it is here (Tampa) and I have never noticed any. Not sure if that is because I do not bother to look, since I am usually focused on about 5 - 6 things I am interested in (and any one's memorabilia would not be on the list).