Research Notes: Unicode Font

I’ve set all the display fonts–library, general, labels, and search–to a unicode font (Gentium).  However, when I want to put in notes taken from a source in the ‘Reference Notes’ field, I only have a limited number of fonts to choose from–plain font, arial, courier new, ms serif, ms sans serif, symbol, times new roman, and wingdings–none of which are unicode.  I need to enter polytonic greek text, which requires unicode.  How do I add a unicode font to this list, particularly gentium?