This one is the OD brake wavy snap ring. Those very rarely break, but it is possible (obviously). Any transmission parts supplier will carry these snap rings; Transtar, PDQ, WIT, Natpro, etc.This is what came out of mine upon full disassembly not including the piece in the pan.
I went thru Cascade transmission for most of my parts as well. This was about 4 years ago so I don't remember what all I got.