One of the catches to this is the intent in which it is sold.

If I were marketing it as though i were pro hate or a Nazi sympathizer then the US government and local authorities could come down on me under the "Hate laws". Using terminology in my ads or my sales that would directly align me that way would be part of it.

If however, a person were selling handles from the showers and ovens or anything along those lines it is deemed illegal. The weaponry, clothing, etc. from Nazi soldiers is very legal and highly sought after for sale or purchase and there is plenty of it that is for sale.