This flea market (Feira de Antiguidades e Velharias de Montijo) isn’t in Lisbon, which means the bargains are better and the finds more “authentic,” if you will. The record bins have been pretty good especially. Take the ferry from Cais do Sodre to Montijo for around €3. See the ferry schedules. The market runs every second and last Saturday of the month. Good for a day of treasure hunting.
If you want to be a seller at the market, contact 21 232 77 55 or dosua_sa@mun-montijo.pt.