IPA letters are more than just mirror versions of regular latin letters, so I tried to make them "real", following the serif rules, etc. For example the /ɹ/ letter has only one serif on top, and the crossbar on /ə/ is at the same height as the one on /e/.  I've only done the Regular weight, but if you're interested I can do italic, bold, etc.

The TTF and SFD source are attached. It's very rough—the letter outlines aren't fused (to make editing easier), and there might be some clockwise/counterclockwise errors. The letters displayed fine in Inkscape though.