First for 'ambulance' in which I got 154 hits, for 'ambulances', I got 185 hits.
Here are two. There maybe more mineable material there.
The Richmond Daily Dispatch: November 25, 1863.
Death from a fall.
--Coroner Sanxay, on Mondayevening last, was called upon to view the body of a dead man who had been seriously injured by a fall the previous night. He ascertained that the deceased was named John Smith; that he was an Irishman by birth; that he was a member of company S, 3d Georgia regiment; that he had been detailed to work as a blacksmith in the ambulance shop, on the south side of the basin; that on Sundaynight last, while in a state of intoxication, be started to his chamber, over the workshop, and, missing his war, fell through a batch, injuring him so seriously that he died the next morning. Smith had on his person $200 in money, and a friend with whom he deposited it gave the Coroner a certificate of deposit of the State Bank of Georgia for $2,800, which Smith desired, after his death, to be turned over to the Sisters of Charity. As the deceased had made no will, the Coroner has taken charge of his effects, and will hold them until some one administers on the estate. Smith has a sister in the State of Maryland, who will probably be entitled to all he has left.
The Daily Dispatch: June 23, 1864.
. . . . Their wagons and ambulances were all filled with wounded, and they were pressing every vehicle into service that they found on the route for that purpose.