Low budget sci-fi short shown on PBS about a store that sold black holes

I saw this in the late 70's or early mid 80's, but it might have been a decade old when I saw it.

I'm sure I saw it on PBS, and it may have been part show, but I don't think the actors in the short where part of the larger show if it was a part of something else.

But in the short a man and women in the future visit a store that sells celestial objects. They have black holes for sell in little boxes. At the end the woman opens one of the boxes, and the screen goes to black after the effect of them all being sucked into the black hole.