Antiques are not only sold in antique shops, but also in ART GALLERIES , in second hand shops, or in street markets. On the street buy for "beauty", not value, and beware of pre-aged "authentic" icons and samovars.
Customs regulations for exporting authentic antiques are strict and you must have a certificate proving that your "antique" is not old or that at least its export will not diminish the cultural heritage of Russia. Good shops will assist you in export formalities. See CUSTOMS REGULATIONS for the formalities of export and APPRAISALS, ART, ANTIQUES, JEWELRY for getting the required documentation.