The group panicked after it was outed by the Age and told its members to delete everything they had posted.
Apparently one member has already been raided and he said he was lucky he was not home at the time.
The group had been peddling handguns and stun-guns, amongst other things. The Facebook group had hundreds of members and made arrangements to buy illegal weapons.
The Age has monitored the page for a week and seen dozens of people have negotiated the sale of swords, knuckledusters, crossbows, extendable batons and bullet-proof vests.
One member of the group said he could get 'dirty' handguns for around $2,000. Another said he could procure new snub-nosed .38 calibre revolvers for $1,100, while another says he can get new 9mm pistols for $5,500.
It took Age hacks a few hours to join the group and be accepted by its administrator so it was not difficult.
The Victoria Police E-Crime Squad said it was not aware this Facebook account existed until they were informed by the Age.
As well as weapons, members of the group were offering prescription medication such as OxyContin, a synthetic opiate.
There is also discussion of committing prescription fraud to get hold of Clenbuterol, a medication used to treat asthma, but which is also used "off label" as a weight loss drug and performance enhancer by athletes.
Facebook said it was policy not to comment on individual groups as when they sign up, Facebook users agree not to use their account for illegal or unethical purposes.