Firms from California, Arizona, and Alaska are listed. There are also a few firms from other states. CalCPA charges firms to be included in this directory, so most likely it isn’t a complete list. I am sure other administering entities (that means the state societies around the country) have a similar list. If you wanted, you could pull in a firm from a different state from where you live.
The AICPA has an area set up on their website for peer reviews.
There is a page to help you Find A Reviewer. There are options to narrow your search down to by state, city, particular practice areas, or industries. I did a search on California and got 20 pages of results with about 10 people per page. There are about 70 firms listed in the CalCPA directory and around 200 CPAs at the AICPA site, so you can make your own guess on how many reviewers are not listed with CalCPA.
As is the case with most things in life, another effective way to find a peer reviewer is ask around.
Full disclosure: you will find me included in both the CalCPA and AICPA lists.