Re: The Y asks for a Certification - Is there one?
I had the same problem with the Y and was never able to get beyond it. A letter from my Sensei, in English, explaining what 3dan meant in aikido, what training I had received, and his personal recommendation that I be able to teach was not good enough. I also supplied a copy of my dan certification and links to the aikikai website, but that still wasn't good enough.
Apparently what they wanted was more of a certification from a nationally recognized organization, more akin to a physical trainer certification. It was all very frustrating because they actually had someone renting space to teach a Tae Kwon Do class! Probably because they saw that more as a competitive sport than a martial art.
However, I think this is case by case. Someone else a few cities over is having no problems with their Y, and another person is teaching at a community sports center and not having any problems.
Good luck to you!