I echo your search and after several years of looking am convinced there are only 2 ways to get any.
1. Cast your own (which is on my bucket list but still a ways down on it)
2. Buy other 80's Hartzell made SUNN gear and scavenge from it (many amps, speakers and PA gear from that period wore the same corners).
When I do get to making a mold and casting for my own needs, I will make several dozen extras and post them as available for the cost of the materials.
Here is a little information shared with me by Rex B who was nice enough to respond regarding the cabinets and trim in that era (thanks Rex B).
"The cabinets on your Enforcer gear were designed slightly after I left Sunn to work at Fender, but I am somewhat familiar with their heritage. The cabinets of this final pre-Fender era were made by a company in Troutdale Oregon called "Bennett". They were done using a technique called Miter-Fold. I looked for Bennett Cabinets in Troudale on Google, and did not get a hit, so they may not be there anymore. I THINK the edging is a stock vinyl extrusion from some plastic fabricator , but unfortunately, I don't know who.
The corners have a more interesting story. Larry Davis, the mechanical engineer at the time, told me he took a plastic stacking Kleenex box, and cut the corners off at a 45 degree angle, (probably on a bandsaw). They used these as a pattern to make an injection mold for the corners. This is why those corners have kind of a sharp edge on them, and undercut toward the cabinet: they really should have beveled them the other direction so they didn't catch on things when you try to slide the cabinet. People have also been cut on them."
