All 64 Minor Glyph recipes currently in the game can be discovered through Minor Inscription Research. You will learn 1 random minor glyph recipe from among all those you are able to learn. If you cannot learn any new minor glyph recipes (because your inscription skill is too low to learn any of the missing glyphs, or because you already know all of the minor glyphs), you will not learn any but will still acquire the by-product scrolls (see also below).