Plugs for Nautilus 801s

I recently acquired a used pair of Nautilus 801s. Like most of the Nautilus line, they've got access on the back of the cabinet to a locking mechanism for the midrange for shipping. On my model, this access hole is covered by a little rubber and metal plug about the size of a silver dollar. Unfortunately the seller only had one of them.

Does anyone here know what might be the best way to go about getting a replacement? There is a single local dealer in my town, but they've been very offish about condescending to order repair parts.

Also, does anyone know of any forums that might be populated with more 801 experts?

Thanks!