NOT a copycat. The only thing remotely similar is that he called himself "the Joker." He wasn't at a theater. He didn't shoot anyone. He didn't have body armor, bombs, or incendiary devices.
He threatened to shoot people at work. Holmes didn't make such a threat.
He had 20 guns and 400 rounds of ammo - at home. That is an average of 20 rounds per gun. Wow. He didn't have any recent large amounts of ammo purchases. Apparently, he doesn't even read gun forums to know he needs about 1000 rounds of each caliber.
No, this guy was not a copycat. He was a disgruntled employee (Holmes didn't work at the theater) who made a stupid threat and played off the incident to gain credibility, nothing more.
Unlike Holmes where it seems still in doubt, this guy really may be emotionally disturbed.
Not currently available, but not restricted ammo either. High speed spire pointed ammo penetrating soft armor should be no surprise.