As an alternative to contacting the company you purchased the knife from, i.e., not ETS, have you thought about just tightening the pivot screw? That usually does a pretty good job of removing any unwanted side play.

Editted to add: I see Brangdon suggested the same thing in the post directly above mine. I skipped reading all of the replies for reasons which many understand, I am sure, so I did not see it before my post. Got to give credit where credit is due.