Thanks for the information, Space Kaijuu. I have recruited the help of someone in Tokyo right now (and of a friend who's frequently there on business trips) to help me look, but it's a slow process.
As for ripping the Japanese tapes, that's definitely on the "to do" list. I'd love to rip the Japanese VHDs at some point since that would give us something as close to DVD quality video-wise as we're ever going to get (barring an official release), but that would be too problematic since I'd have to find a VHD player to do that...and those things cost hundreds and hundreds of dollars.
I have seen the complete set of episodes that you mentioned on the Spleen, but the last seven episodes especially are in extremely lousy shape and come from a second or third generation copy of fan-distributed bootlegs that were making the rounds as early as 16 years ago. I remember picking a copy of one volume up when I was at San Diego Comic Con way back in 1998.
Right now, the plan (such as it is) is to take the Japanese video and combine it with the English audio from a first generation TV recording that a casual acquaintance of mine, a seasoned professional from the North American animation industry, received from a friend back in the 1980s (provided he can find it). Granted, this will still leave us with a few burned-in subtitles from the Japanese version, but I think the dramatic increase in quality will be worth the trade-off.
One extremely frustrating thing, though, is how massive a financial drain this project has become. I've already spent at least 150 bucks out of my own pocket tracking down multiple versions of all six North American home video releases and purchasing two working JVC Super VHS VCRs to squeeze every last ounce of quality I can from the old tapes, to say nothing of the dozens of hours I've spent ripping the cassettes using a Dazzle video capture device, editing the footage together, and scanning and photoshopping the old inserts.
It's really a shame that this forum frowns upon selling fan restoration/preservation projects. Considering that one eBay seller has already sold several copies of his crappy torrent download version of the show for 26 bucks a pop, it would've been nice to at least have broken even on the one I'm assembling, especially considering that TMS and MGM have no plans to ever release it on DVD or Blu-Ray.