Well, I did some more sleuthing and found the parent companies for Endura-Tech: NHK INTEX Coproration and their parent company NHK Sales Co., LTD.
So I sent an email to NHK Sales Co via their "Contact Us" link last night. Tonight I checked my email and received the following reply:
Thank you for your interest in the Endura-Tech Products and having used our coilovers.
Unfortunately we stopped manufacturing and selling the coilovers, tower bars and replacement springs in early 2011 due to the increased material cost as well as the unfavorable exchange rate to us between Japanese Yen value and US dollars.
In early July we ceased posting the website homepage.
If you have any other questions, please let us know.
Best regards,
Katsuo ken Matsubara
NHK Intex Corporation
So now we know.
It's time to Frankenstein some rear coilovers then...