I'm glad you have plan to go those shops. Sorry that I don't have the map with me now. Can I try to tell you how I usually go there (though I'm not good in giving direction)? From Piccaddilly, walk to Shaftesbury Ave. When you see the theatre that plays Les Miserables, turn left onto that little alley and within one block or two, you will be on the street named either Brewer or Beak Street --- sorry I can't remember this part exactly, and hopefully you will also see a parking building at the opposite corner. Then those little shops would be on the left hand side. Walk toward that direction and pay attention to the shops on both sides. I hope you will see them before you hit Regent St. Hope you also enjoy the shopping.
I can spend an hour in those little shops, seriously.
The map you displayed here is the other side of Regent Street. Those little shops can't be seen from there. But the bigger one, i.e. 3-storey Japan Centre, is right on this map, on Piccadilly, in front of a crowded bus stop. .... I wonder if you know this one.