Gun City owner David Tipple confirmed this week that the alleged gunman had bought firearms and ammunition from his store but Tipple said he had not sold the semi-automatic weapon used in the killings.
Reloaders general manager Scott Stonex confirmed his store was co-operating with the police investigation.
"We have disclosed any relevant information to the New Zealand police," he told Stuff.
"We are co-operating fully with the New Zealand police and answering fully their questions and queries.
"And we have no further comment at this point. We do not wish to prejudice the investigation or any other legal proceedings."
Asked if Reloaders had sold the fifth gun used in the shootings, Stonex said: "We don't know. I can tell you we don't know anything yet. That is where we are."
In a statement, a police spokeswoman for police said: "The investigation team is making a large number of inquiries, both across New Zealand and internationally. While the investigation is ongoing we are not in a position to go into specifics around those inquiries.
"The matter is now before the Courts and we will not be jeopardising any future prosecution. All of the detail will become part of the Court proceedings."
The Government announced today that military-style semi-automatics and assault rifles will be banned under new stronger gun laws.
It is offering an amnesty period and buy-back scheme but is moving immediately to stop people stockpiling the weapons.
The accused man obtained an A-category firearms licence in November 2017.