The NRA-ILA says that it filed the Opening Brief for Petitioners.
NRA-ILA | NRA-ILA Files Opening Brief in Second Amendment Case Before the Supreme Court
This makes sense given that the attorney of record is Paul Clement, the NRA’s go to attorney for Second Amendment cases. Therefore, I do not expect to see an Amicus Brief from the NRA.
Note well. Backing litigation like this with the best legal talent available is at the heart of the NRA’s mission and a sufficient reason to support the NRA (and why we should never bash the NRA in public).