I used to live in Moscow for more than 20 years. Actually, I was born there. And I visited St. Pete so many times during my school and university years, I can imagine how a tourist feels like here.
Now, as I’ve been a citizen for more than 10 years, I know where to find things. But then, I’ve had concerns I couldn’t cover. For example, once I came to St. Pete for a week and my boot laces happened to be torn. I was walking around uncomfortably for days looking for the new laces and found this small repair shop. It’s the easiest way to find laces of every color (they also repair shoes) in the center of the city. Since then, this shop is my friend. I come here for a new pair of laces.
There are also some interesting antique metal shoe-repair-thingies inside. And the staff is nice, too (not always English-speaking, though, but you can point to the laces of your choice and smile).