buying soviet stuff in St Petersburg

I am going to visit st Petersburg next summer and since I will be only 2 days there where is the best place to buy rangefinder cameras and lenses without expending too many time. I already own a zoki 1 an industar 22 and an industar 26m but I want to buy a shorter (jupiter 12) and maybe a longer lens. ( and visit the GREAT Hermitage and.... not enough time...)