@momma2a - the Unifieds website only lists the “official” members of Unifieds, and up to 2 times as many non-member schools hold auditions in Chicago (I think somewhat fewer in NYC, but still many more than on the “official” list, not sure how many non-member schools attend in LA). Hence, there is no single source to go to where you can easily determine all the schools that will attend Unifieds. For non-member schools, you have to check with each school that you are interested in to see if they will be holding auditions at one or more of the Unifieds sites. Some of the non-member schools only hold auditions at 1-2 Unifieds sites, so the list of attending schools will vary considerably between each location.
The Unifieds website does provide a way to confirm the attending official member schools.
If you look back at the Unifieds threads from previous years you can see ad-hoc lists posted that will give you some ideas of what schools to expect, however, attending non-member schools are going to vary from year-to-year and location-to-location so no list that you will see will ever be comprehensive and correct for the coming year.
Here are some posts with lists from previous years:
http://talk.collegeconfidential.com/musical-theater-major/1855408-nyc-unifieds-school-list-2016.html
http://talk.collegeconfidential.com/discussion/comment/19094128/#Comment_19094128
http://talk.collegeconfidential.com/discussion/comment/18929126/#Comment_18929126
There are more, these are just the ones that I found with a quick search.