Get a power supply that can output a regulated 12 VDC and 5VDC; a PC power supply can do this, but may need a bit of load on the 5 volt rail to maintain regulation. You might, instead, find a regular power supply from someplace, like this one:
I'm not saying that will work for your purposes (since I don't know your current needs); I'm just showing you something for illustration.
Now - you may be asking "Where do I get my 7 volts?"
Well - you only have one device for that need - so, provided you can isolate it from the rest of the system (that is, not have it's ground connected to anything else) - you can hook the 12 volt output to it's positive supply input, and the 5 volt output of the supply to its ground input (12 - 5 = 7); essentially, the 5 volts is the reference for ground for the device (but whatever you do - DON'T TRY TO HOOK THIS UP TO ANY OTHER GROUND - you'll short the power supply).
If that won't work for you (which it might not), you could instead hook up an LM317 voltage regulator (for the needed current) to the 12 volt, and adjust it to output 7 volts for the coin acceptor (you'll probably want the TO-220 package and a good heatsink - or you may look into a switching regulator for this task).