Gary Hyde, 43, of Mask Lane, Newton on Derwent, near York, was convicted by a jury at Southwark Crown Court of breaching British trade controls.
He moved the weapons without a licence and hid more than $1 million (£620,460) in commission payments, Her Majesty's Revenue and Customs said.
The court heard that the shipment was made up of 40,000 AK47 assault rifles, 30,000 rifles and 10,000 9mm pistols, along with 32 million rounds of ammunition.
Mr Hyde was convicted at retrial of two counts of becoming knowingly concerned in the movement of controlled goods between March 2006 and December 2007.
He was also found guilty of one count of concealing criminal property between March 2006 and December 2008 after he was alleged to have hidden the profits in a bank in Liechtenstein.
Mr Hyde, who served as a special constable for seven years, will be sentenced on November 23.