Never mind. I resolved it myself. What I needed to do was put the fonts in my User Font folder instead.

I've recently added many new fonts to my computer (It's a Mac). I've put them in the folder /System/Library/Fonts, as I was under the impression that Inkscape took fonts from that folder. But none of the new fonts are showing up in Inkscape. Is this a known bug, or am I doing something wrong? Thanks...