You can easily find stores in Namdaemun Market that sells this street food. I went to this store located near Gate 3 in the market that sells both sweet and savoury versions. Sweet hotteok (krw1000) has a mix of sugar, honey and nuts whereas the savoury one (krw1000) is filled with japchae - glass noodles, carrots, and spinach. The deep-fried hotteok is chewy and a trifle oily, so might want to share this!