Dave: It isn't all that expensive, and you may do it yourself if your practical enough
I replaced one top plate of my 4000 and did it myself, the one plate cost $90 aus dollars. The top and bottom peel off (and are destroyed) the front panels can be easily unscrewed once the grilles are detached.
Yes you can order those plates no problem, so long as you are aware of how much concentration you'll need to put into it, once the glue on the plates comes into contact with the speaker cabinet, that's all folks! So be careful. I did a very good job of mine. Hey, in all honestly, save yourself some money and forget the bottom plates, no-one see's them!
“Quality is never an accident; it is always the result of intelligent effort.”
Your health and well-being comes first and fore-most.