Well, I continue my rummaging throughout piles of computer detritus at my work. And today my search went successfully.
I've been told that ages ago, before my time, my company was using a lot of Wyse terminals. They were all scrapped, but I managed to salvage sole remaining keyboard.
It's Wyse WY85 Gate Array with Cherry MX Black. Dunno when it was manufactured... It's dirty, of course, but not near as bad as my last find. Aside from that, it almost in pristine condition. Key labels not worn off and there no big scratches on case.
As it is terminal board, it, of course incompatible with regular PC... but maybe I can use the fruits of Soarer's hard work?..