Cash and cigarettes were taken during the robbery at Hyperama in Richmond Street, West Bromwich, on April 9 last year.
Dean Berrington, Satnam Singh and Brandon Morris are now waiting to be sentenced at Wolverhampton Crown Court after a jury found them guilty of conspiring to rob the business.
Masked robbers, armed with a gas-powered air pistol and baseball bat, targeted the warehouse at closing time.
The trio were found guilty of conspiring to rob Hyperama between April 1 to April 10.
Paul Bardsley, another defendant, had already pleaded guilty at the start of the trial.
Jay Brownhill was also allegedly involved in the robbery but he has since died.
Morris, aged 22, from Lellow Street, West Bromwich, was also found guilty of possessing an imitation firearm.
All three denied the offences ahead of the trial. They were given bail after the jury handed out their verdict.
Judge Amjad Nawaz told the defendants: “There will be a custodial sentence. But I am still to decide how long that will be.”
The trial heard there was a five-strong gang involved in the robbery. It was claimed that the raid was an inside job and the gang had been given vital information.
Berrington, who worked at the warehouse, and supervisor Darvinder Kang were locking up the premises when the raiders came in through a side exit.
Both men were tied up at their hands and feet while the gang ferried pallets of cigarettes on trolleys to a Hyperama van, for which they had the key.
The Mitsubishi van - loaded with the stolen haul - had a tracker which enabled police to follow its route.
It took officers to the home of 52-year-old shop owner Singh in Jesson Road, Walsall.
He was found in his garage behind boxes of cigarettes from Hyperama.
Berrington, 41, of Crankhall Lane, Wednesbury, Singh, and Morris will appear before court on December 5 for sentencing.