A start at least: Washington Post
The world's largest retailer, Walmart, announced a change to its policies Wednesday, saying it would raise the minimum age required to buy a firearm and ammunition and remove any items that resemble assault rifles from its shelves.

In a statement, the company said it would raise its age requirement to 21 from 18, a decision it made "in light of recent events" — most notable the national discussion about gun control since the Feb. 14 shooting at a high school in Florida that left 17 people dead.

"We take seriously our obligation to be a responsible seller of firearms and go beyond Federal law by requiring customers to pass a background check before purchasing any firearm," the company said.

Of course, taking items 'which resemble assault rifles from its shelves' does not mean quite the same as stopping selling them.
But the change in age requirements is a good start.