Rear seat for a 21' ultra...maybe side  panels too

You’re more than likely never going to find a matching set in good shape that will fit your boat. I’d reach out to an interior shop and get quotes for those pieces. Where are you located?

San diego

Look up Temecula Speed and Marine. There is a guy there by the name of Raul that does great work. I hear he’s reasonable as well. He does all of Essex’s boats.