The only thing (on NA17) that seems to consistently drop medals is an NPC10 (and that is almost entirely Nation/Justice, which won't people don't need yet even when they CAN farm 10's). I hit level 10 valleys all the time and don't seem to get much at all. I coined (somewhat) to around Duke and then I had enough high level medals to more or less make the jump. 20 away from Prinz.