We've (muaythaimall.com) have opened up a shop not far from Sutthisan MRT station in the Ratchada area of Bangkok. Basically we've converted our office into a shop as well as a lot of people were asking if they could come pick up gear while they're in town.
Our location is on the other side of Bangkok compared to most Muay Thai shops like Actionzone, Boon and Top King. We're not too far from Chatuchak park / Ladprao or Asoke (by train).
We carry most brands Twins, Fairtex, Top King, etc. Our office/shop is on the corner of Soi Sittichon and Sutthisan Rd. It can be a little tricky to find us as we're on the 2nd floor of the building but our google maps location is spot on!