Mapex Orion add-ons are just hard to find. They were a series released by company that was not well received when they came out. Mapex 15 years ago is not what they are now. The Orion series were not big sellers because they were the same price, if not more, than established brands. Aside from the outlets you mention, I wouldn't even know where to look.
What are you looking for so I can keep an eye out?
I'll keep an eye out for any Orion series in those sizes with chrome hardware. They really are good drums, but they weren't sold in big numbers, and the majority have the gold hardware. I have a Brass Master 14x6.5 snare with the 24k (afaik) plated lugs and die-cast hoops from that era. It's an absolute killer.
Dang! That's a hell of a deal, especially from the BSO. You will find what you're looking for eventually, and I'll try to help you out. That is a great shell bank.