Someone fit a storm enforcer side panel on their haf 912. The bad news, it looks like cm's out of stock on that one too.
http://linustechtips.com/main/topic/4671-storm-enforcer-window-on-haf-912/
This may be a long shot, but have you tried contacting cooler master? My suggestion would be a phone call (rather than email, seems most email requests get lost or ignored). It's no guarantee, but in the past with other companies I've called not expecting much success in getting out of stock or no longer available items and been surprised. Even things that may not be listed on the website. Awhile back I needed a new front air filter for an antec case (old sonata II) that was discontinued and also needed some of the rubber grommets used for mounting hard drives to the trays. Gave them a call and customer service was really nice. They shipped out both at no charge. Doesn't hurt to at least ask, there's always a chance they might be able to help you out somehow.