More amicus briefs
38 State Attorneys General, stressing a due process approach. National Shooting Sports Foundation's amicus, which is mostly devoted to the 2d rather than the 14th Amendment. 900+ State legislators, arguing for due process incorporation. And here's Maryland Arms Collectors' Association, arguing for due process and Nordyke's approach.
And here's Calguns Foundation, hitting at Charles Fairman and Raoul Berger, who argued against privileges or immunities. Their view was dominant from about 1949 to the 1980s -- as in when I went to law school -- until Michael Kent Curtis came on the scene and bested Berger in a number of law review debates, re-establishing privileges and immunities -- all the more remarkably since Berger was then a very big-time law prof, and Curtis a fellow in private practice doing this in his spare time.
Several more, but not yet in online form (it's lots simpler to link to a document already online than to upload one).