If they are round ports, you might google "expandable test plug". It's a plumbing part. That's what I use.
Duke
Speaker Bass Port Bungs
Does anyone know of a company or manufacturer of bass port bungs for speakers. Or is there way to make your own and if so what material is best to use to control mid bass. Socks are not the answer! Looking for a type of device to use on my rear ported speakers.