Most Gulshan 2 Market shops are open from 10-7 daily and closed on Sundays.  Sports Time offers a small selection of Prince rackets, a variety of kit including balls, bags, clothing and shoes, as well as a stringer.  If you have your own string reel, bring it in and they’ll string your racket for 100tk.  Otherwise, stringing is free when you buy their string.  When you go there, just ask for Mahbub!