Ummmmm........I live in Massachusetts. I lived for a number of years in Concord, where it all started. Today I live two towns away from Concord. There is a lot of information available about the militias and the Minute Men and the Battle of Lexington and Concord.
The muskets used by the Minute Men were their personal possessions, not issued by the government and not crown possessions. Isaac Davis of Acton, one of the first men to die at the bridge in Concord, was a gunsmith who had made his own musket and supplied each of the men in his company with a bayonet. There were gunsmiths like him in every town, and there were gunsmiths and merchants in Boston with large inventories of firearms. In the weeks after the Powder Alarm in September of 1774, and before martial law was declared in Massachusetts, it has been estimated that as many as 100 muskets and pistols per day flowed out of Boston into the hands of the militias.
Militias in New England go back much further than the Revolution, they go back to the founding of the New England colonies, 1620 for the Plymouth Colony and 1628 for the Massachusetts Bay Colony. In those days the colonies acted almost completely independently of the Mother Country, running their own affairs, including raising militias. Colonial militias were very democratic, the officers were elected by the members of the militia. Local militias were very active in King Phillip's War from 1675 -1678, fully one hundred years before the Revolution. By the time of the Revolution, the only place where the British Government held any sway was in Boston itself, which was occupied by British troops. In the country outside of Boston, sentiments ran strongly against the British and what few Tories there were kept silent for their own safety. The various town militias most certainly were not sponsored by the official (British) government at this time.
Minute Men were the cream of the crop of the militia, less than 30 years old and selected for their political beliefs and enthusiasm. They were the rapid deployment force of the day, ready to turn out rapidly 'at a minute's notice'.
What happened at Lexington and Concord on April 19, 1775 was the British sent a force out of Boston to confiscate rebel arms, powder, and supplies that had been stockpiled in Concord. I used to live just down the road from the Barrett Farm, where many of the muskets as well as some purloined cannons were hidden in the fields. The Regulars defeated a small force of militia on the green of Lexington at dawn. Then they marched on to Concord about six miles away. A small scouting party had crossed the bridge over the Concord River and reached the Barrett Farm, but they did not succeed in finding the arms hidden there. The scouting party made their way back to the bridge when they realized that hundreds of Minute Men and militia were forming up to meet them. The shooting started at the bridge and the colonists drove the Regulars all the way back to Boston in a running skirmish that lasted the rest of the day.
As for modern replicas of the muskets used in the Revolution, here are a couple.
http://www.dixiegunworks.com/product_info.php?cPath=22_92_186_190&products_id=957
http://www.dixiegunworks.com/product_info.php?cPath=22_92_186_190&products_id=956
