This guide lists what briefs for different courts are generally available in the Gallagher Law Library and in online sources like Lexis and Westlaw. For example, we'll say that Washington Supreme Court briefs up to 1988 are in paper, and then we have them in microfiche, and after that they're available online.
In addition, you should remember that someone might have collected the briefs for one case, perhaps digitizing them and posting them online. For example, the William A. Wise Law Library at Colorado Law has gathered and posted material related to Arizona v. California. Some collections include material other than briefs, such as newspaper clippings, correspondences, and photographs.
We list a few of these collections on particular cases below.
To look for a collection for a case you're researching,
Some nonprofit organizations and professional associations post briefs they have filed. Reading the briefs may be a good way to pick up interdisciplinary sources—e.g., the American Psychological Association's briefs cite studies bearing on the issues of the cases.
The following list is just illustrative. There are probably many other organizations with collections of their amicus briefs. Some organizations issue press releases and sometimes post amicus briefs individually without having a page collecting them.
If you think an organization might be interested in the case or issue you're researching, run some searches and check its website.