There may be other sources, but if you're talking about on Talkin' Broadway:
We got rid of the performance schedule information a couple of years ago. It was too difficult to keep up with changes (most or many of which were not publicized) and we got complaints when, consequently, the information was not up to date.
If you're looking for a Sunday performance for a specific time period, start a thread about it - that usually generates good information. There are some Off-Broadway companies that traditionally offer Sunday evening performances (like the Public).