Reading this thread made me wonder: how does one go about getting a nice transparent plastic box to protect a cardboard box?

I actually have a board game box (slightly smaller than a DVD and around twice as deep) that's falling apart and I've been thinking that a suitable plastic thing would be just the ticket, but I'm at a loss as to where to find one. But if there's an industry for producing these things for old video games, maybe I can find something suitable.