In Southern California, someone is selling a 1993 Humvee on eBay and Craigslist that looks ready for overseas action — the beefy, diesel, tan-colored armored vehicle comes with a CB radio and a gun turret. The price is real, at $40,000, but the .50-caliber machine gun mounted on top is fake, the person selling it writes in the descriptions. The Humvee appeared to have a new starter and power steering gear, but the age of the smoke grenade launcher was unclear.

“I am an active duty U.S. military member,” the seller wrote on Craigslist. “I do not have time for tire kickers or dreamers without money.”

Online, one can buy a camouflaged Humvee with an enclosed rear shelter unit or a 1997 SWAT van ($5,000) that the seller claims was used by the City of Southlake, outside Fort Worth.

It was unclear how often the suspect in the Dallas attack, James L. Boulware, 35, drove his armored van. Mr. Boulware’s father said his son referred to the van as an R.V. and often slept inside it. Though numerous similar vehicles were available for purchase online, several of them were not in driving condition — like Mr. Funicello’s armored truck — and it was impossible to determine how many others like it were on the roads.

Officer David Tilley, a spokesman for the police in the Dallas suburb of Plano, said he was not aware, in his 18 years with the department, of officers having any contact with anyone driving a similar armored van.

“Had we run across something of that nature that wasn’t commercially operated, such as armored vehicle services that collect money from banks or businesses,” he said, “I am certain we would have put out an officer safety bulletin on it.”