Tzar's Tzar, with no Tzar - Leonid Sinitsin's one of the kind cartridges from Angarsk, Siberia... Thanking Erik M. for the finding.
Mr. Leonid Sinitsin, the one and only artisan able and skilled enough to restore any DST-design cartridge. Just in case... as a plus, he hand-made quite interesting more conventional cartridges, as well. Just don't ask for a direct-sale of Tzar's;-) - its worldwide sole-agent is Robyn Wyatt, in the USA.
I repeat: above is a serious advice, so please don't ask for!