I would guess that spring clip panels are available at Partsexpress here. (Check page two of the results also)

Edit: Maybe this one in particular?

If you can't find one the exact size, you could always "plug" the existing terminal plate space with a block of wood and mount the new plate over a larger block of wood.

It looks like you've already unscrewed the terminal plate to check it out....

Last edited by MarkSJohnson; 11/11/10 11:26 AM.
::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::