At a guess, you did not use a Ta aspect rune for the glyph you made. Only Ta will work for enchanting writs. At least there is a place to use these up.

You can check guild stores for runes. No NPC vendor sells them. You can also buy and or loot glyphs and deconstruct them. The more points you have in extraction, the better your chance of getting runes back. You should be deconstructing glyphs anyway, as it's the best way to level enchanting. As for finding runes, all resource nodes respawn in the same locations. If you learn these sites, you can make a circuit and pick up a lot of resources. For runes, the node can respawn as any type of rune, so for best results harvest all nodes, even those you may not value, for a better chance at ones you do value. Chests are also a good source of glyphs for deconstruction. They also respawn in same locations, creating another farming oppotunity.

Um, it's been a little while since the last time I did that certification quest, but I don't think it's a trifling fire glyph you're supposed to make, I think it's a trifling health glyph.

Thanks. You were right! I somehow confused fire and health...