@mja2500 were you able to fabricate a lock down bar or find an equivalent? I'm in the same situation right now, trying to track one down or figure out a workaround.
That thing is very very very similar to the bar that's used to hold the backglass in a bally pinball machine at the top of the pinball head. It's likely shorter though, but you might be able to grab one of those and make it the right size.