You can call Miles Fiberglass and ask them. You might get somewhere. If the military orders a fiberglass enclosure the kit will come with a parts list on paper. Finding that parts list outside of finding the paper included with the hard topper kit or getting it from the manufacturer is the only way I'm aware of. I doubt TACOM will assist you unless you know people and if that were the case I feel like the question wouldn't have been asked.
If your plan is to look for a surplus example - good luck. These are generally build to order, are tens of thousands of $$, and any unit that disposes of a truck with one IS going to pull it and put on another truck. And keep doing this till it's literal trash. Because these are not generally found on MTOE - they are ordered by the unit assuming they have a need AND the funding and command at a couple levels agrees on that need...... they are RARE and typically only seen in very cold weather environments. Few are produced and I'm not aware of a single one that has got out.