I can't imagine it would be so hard to find the parts needed, unless they're very special in some way. Have you been searching for the specific part or instrument number, or just side panels in general? You may be unnecessarily limited by looking for low-volume items. Once you know the right size and ventilation arrangement, you may be able to find something off a high-volume, common instrument type, and identify it from pictures and descriptions.
I'd guess that the 5-1/4" H rack size is the highest runner of all time, so there should be a lot of stuff out there. The 19" is probably the most common depth, also. For example, the HP 8566 and 8568 SAs, and their accompanying 85662 IF/display units are very high runners, and there are a lot being parted out regularly and offered on auction sites. I believe they are the size you're looking for, and are fully-vented - the non-handle sides have hundreds of holes, front to back and top to bottom, and the handle sides have the same, except for the handle strip down the middle. I see them nearly every day, out in the garage. At the other extreme, sometimes the best deals for chassis parts or complete units are to find way too obscure or esoteric obsolete instruments that nobody needs anymore.
Ed
