kbear
Sorry to correct you, but PRS+ is not available for models 700 and 900.
@julo
But you may search on
the-ebook.org for a "russification package by boroda (aka porkupan her at MR) or amutin. - Use google-translate if needed.
This mod fw is primary meant a enably support for Cyrillic, but it embedds a modified font, maybe supporting also your missing glyphs.
Otherwise I see no other way as to go with CSS and calibre.
HTH
Mark