Your best bet is a tape measure and a junkyard. Here is a poor pic of a 46 with the back seat out of a BMW 4dr. Looks decent but don't know year or model (lots of help!). Some have used third seats out of an SUV but once again I can't name the year/model. Hopefully others have paid closer attention.
These seats are from a 2001 Silverado, the console is from a Dodge Durrango. This photo is from the start of the project, built I think they will look good, plus have 3 point seat belts as part of the seat.
My Chevy 2004 Trailblazer has some nice bucket seats in it, After 200,000+ miles they're still in great shape. Not to mention, we aren't small people over here. They have the belts built into the seat also. The lower brackets are different heights to accommodate the tunnel, so some fab work is in order to fit them into anything.
I think your biggest challenge will be the room in the cab, both narrow and lacking leg room. Maybe third row seats out of minivan or mid size SUV. Might have to source a seat/seats with a somewhat thin backrest.