Interesting...I was going to post about this, but I forgot. The last time I was there, about a month ago, it seemed like they'd changed sources. The onion roll, for example, was larger (longer) than it used to be, tougher, and less tasty.
There is a bakery in Bklyn, not far from the restaurant, where they have long purchased their rolls. Unfortunately, I don't know the name. But, your question is a good one. Their onion rolls are absolutely the best.