Aurora U-Pull has about 5 E350's 2000 and newer, I was there Saturday. I got the last steering dampener bracket in the whole yard ($8). I didn't see much for seats in the vans, some had quite a bit of their interior plastics left...
I sold all my bucket seats from my van on CL.
Also, you might get a hold of a few of the van shops around Denver, Key Fleet Resale, Denver Fleet, Boulder OffRoad. They may have some spare seats around.
2010 Ford E350 EB 6" Weldtec Lift
2017 Subaru Legacy
1990 Volvo 240GL
2x 1987 BMW 535is
1995 BMW 540i6