Here is the opinion in Yellen v. Confederated Tribes of the Chehalis Reservation.
Here (the remainder of the briefs are on the Yellen v. Chehalis backgrounds materials page):
Here are the merits briefs:
Amicus Briefs Supporting Petitioners:
Amicus Briefs Supporting Respondents:
Cert Stage Briefs
D.C. Circuit materials:
District Court materials:
Here is the order in Confederated Tribes of the Chehalis Reservation v. Mnuchin (D.D.C.):
Case tag here.