Captured British Ordnance: As the war progressed, the colonists managed to capture British ships, forts, and arsenals, gaining access to their heavy cannons and other military supplies. This was a significant source of artillery for the Continental Army.
French Assistance: France played a crucial role in supporting the American cause, and one of the ways they did so was by providing military aid. The French supplied the colonists with heavy cannons, among other resources, through covert operations and official trade agreements.
Local Production: Despite their limited industrial capacity, the colonists made efforts to produce their own cannons. Iron foundries and workshops were established, and skilled craftsmen worked to cast and manufacture heavy guns. Some of these guns were made from melted-down church bells.
Privateering: American privateers, essentially state-sanctioned pirates, played a significant role in harassing British shipping and capturing British prizes. In the process, they sometimes managed to seize British cannons and bring them back to the colonies.
Donations from European Sympathizers: The American cause enjoyed sympathy and support from certain individuals and groups in Europe who were opposed to British policies. Some of these sympathizers donated or facilitated the purchase of heavy cannons and other military supplies for the colonists.
The colonists' ability to obtain heavy cannons was an important factor in their ability to wage war against the superior military might of the British. Cannons were crucial for both defense and offense, enabling the colonists to fortify their positions, attack British ships and fortifications, and engage in artillery duels on land.