DCM chair, replacement plywood?  

There is a secondary market for them but it won't be much of a cost advantage over purchasing a complete chair
The upholstered plastic version of the chair, the EC127, beats the DCM hands down for practical daily use. The padding provides much comfort, there aren't any stupid mounts to fail, and they can be found in some great colors. I sit in this chair model more than any other, at my table and desks.

Put cowhide on it and be happy!

You can find replacement pieces on eBay. I have a couple of spare seats. The plastic version may be more durable, but the plywood version is much more beautiful.