I cannot answer for certain but in many instances, items such as this were fabricated as a cottage industry for someone who was retired and looking for some extra hobby money. Alot of times, the person just 'ages out' and so the product ceases to be manufactured.
I would call and talk to Don Snyder to find the information as he likely knows. If none are available, then maybe find a local sheetmetal fabrication shop to make one for you.
As far as being able to access them, I feel that most people (-except those who may be a little vertically challenged
) can likely access them from standing on the outside and leaning into the back section. Cutting the rear floorboard into two sections might make lifting the mat and floorboard easier. As far as condensation, I'd say that temps get pretty warm inside the box with the muffler body running parallel to it.