That was the only source of BG razor production back in the days AFAIK.A couple more of these amazing razors have turned up on the bay and the sellers say that these razors come from the TPK "Brotherly Labour" (workers co-operative) steel casting factory in Sandanski.
Here is another set that just was on sale (priced at about EUR 15):
Аукцион.БГ: Стара самобръсначка ТПК "БРАТСКИ ТРУД"САНДАНСКИ,соц.