sturdy box lid (Britannia)

Does anyone has a fitted box lid they no longer use?

I'd like to create a solid top for this flimsy little table – this lid I have (see pic) would be great, except it's just a bit too small.

Ideally, I'd like a box lid that's at least a foot square – larger is okay, I can cut it down to size.

It doesn't have to be very fancy, either, since I plan to cover it with fabric.

Hoping someone can help!

Thanks,
A.