It is hypothesized soldiers throughout history took local "monies" i.e. coins and put them in personal forges or presses to make desired items such as spear heads, fish weights, musket balls, bullets, military figurines, or new repurposed coinage and tokes. This activity had two purposes. First. it had a negative impact on the enemies economy. Second, it generated difficult to obtain items soldiers needed or wanted. So a good place to start if you seek to mint your own coins; is places that sell equipment to make items like the ones in the list above. Maybe take a class in how those hobbies work, and what basic minting or forging equipment is needed. Don't be afraid to ask the practitioners how they make souvenir coins in their particular craft. They have all probably tried it, seen it done, or heard a particular methodology. You don't have to make on like your planning to set up a major counterfeiting ring. Letting people know you'd like to know how to make souvenir coins is fine. You might just get your answer. Best wishes.