I live relatively close to Sun Valley, and there are a bunch of dismantlers along with pick and pull parts places. But most don't have anything Mitsubishi. I found this out today while I was looking for anything Mitsubishi Montero. During my search I was referred to Pit Stop Auto Wrecking on Brandford. These guys have a whole bunch of Monteros (all generations). They also do Subarus. I'm not affiliated with them and I didn't find the seat I wanted, but if anyone in SoCal has a Montero need it might be worth calling or visiting them.
BTW: They are open on Saturdays, not sure of the hours though.
BTW: They are open on Saturdays, not sure of the hours though.