I've been doing a little online research and chanced upon Dušan Šuráni's vintage diving history website at
http://www.vsc-ds.cz/
The site is in Czech, but text can be easily if roughly rendered into English by running it through Google Translate. It contains plenty of illustrated information, including images of, and texts for, two pages of double-hose regulators including some of Czech, Polish, East German and Yugoslav origin:
http://www.vsc-ds.cz/sbirka/dvouhadicov ... regulatory
Hope this is new to everybody and therefore may be of some interest.