Small alley in the center of Busan holds a few exchange kiosk with best rates and no passport showing. The place I marked on the map below. Hope it helps.
https://www.google.co.kr/maps/place/Useongsa/@35.099491,129.0287187,19z/data=!3m1!4b1!4m5!3m4!1s0x3568e9a0765ac54d:0x50a9da9747a228ac!8m2!3d35.099491!4d129.0292659?hl=pt-PT
https://www.google.co.kr/maps/place/Useongsa/@35.099491,129.0287187,19z/data=!3m1!4b1!4m5!3m4!1s0x3568e9a0765ac54d:0x50a9da9747a228ac!8m2!3d35.099491!4d129.0292659?hl=pt-PT
