they cleaned up BKK quite a bit. only at MBK can u find such dealers. with regards to quality, your mileage will vary. be prepared to bargain very hard, the thais come across as very hard bargainers, far harder than chinese.
Siam Paragon is all high end... so don't expect to be finding stuff like reps there. there used to be another mall doing all such stuff but it has since been redeveloped.