I used to use one of those all the time until I got my smart phone as the dictionary on it is as good as the dedicated dictionaries.

But, to answer your question I bought mine in 전자랜드 (Jeonja Land). They have stores all over the place, but the biggest I know of is in Seomyeon. Map here http://me2.do/51GEwhNz. Exit 6, double back on yourself and head toward the road that leads to Migliore.

(click 'X' in top right hand corner to revert to map view)