Before we go into detail on how coins are actually made I think we'd need to see you make a prototype using the 3D printer first to see whether it can actually be done otherwise you'd end up wasting money if you didn't know whether or not the printer worked well in making coins, the reason I say this is because I'm not 100% convinced that a 3D printer is capable of doing such detail on the metal just yet but I'd be happy to be proven wrong on this point.
As for the fairly traditional methods of coinage I actually did quite a bit of research on this and I can show you where to go for the coin dies and the machinery, as it so happens machinery and tool wise everything seems to have re-located overseas so you shouldn't have too much problem finding companies that make hydraulic presses, I also happen to have found a guy that is still in business making coin dies, beware though, the coin die is pretty expensive but this person is a proper professional, make sure you're completely happy with your design before you submit it.
http://www.satishhydraulic.net/frame-type-coining-presses.html - This looks like a pretty old and well established company, I haven't tried contacting them yet but there are quite a few Indian companies out there that making presses some even doing custom orders
http://www.ringstamps.com/coining_die.htm - This guy is located in America and responded to my emails when I asked him about cost and the process of making everything, he said it varied from $300 - $1000 per side, so if you want to have something stamped on the back as well then you'd need to pay twice.
The method I'm thinking of uses a mixture of traditional clay casting to make blanks and then the hydraulic press, I haven't yet tried it though because I'd need to get money together, you also need to bear in mind like me you have no reputation and it looks like it's pretty damn difficult to sell anything here unless you've got positive reputation already so you'd have to look at some kind of cheap product to sell.
Also, here's where I got my idea from, it would be pretty simple to get the right diameter to match the coin press:
https://www.youtube.com/watch?v=b6T_ZutXzNQI may actually try this method entirely by hand but I'm not 100% sure whether it will work, hydraulic presses seem to be the modern way to go because you need a certain amount of tonnage in order to make sure coins get properly stamped with the die and hydraulic presses mean one person can essentially do the work without too much trouble or effort, not only more efficient but it's supposed to be safer to use the hydraulic press.