Turn Signals - Driving me nuts!

If the bulbs are new and are known good, sometimes the sockets need cleaned or replaced the connections get corroded etc. you could do a wiggle test turn on the left side for example and gently wiggle the bulb see if it starts flashing etc. other than that basic test get a test light and probe deeper once on the right circuit your test light should flash then at least youd know if your flasher is feeding the front sockets.