Way to be helpful and show your internet superiority Rebel
Pete, tray calling around to whitewater rafting companies in your area, or even far away ( a thwart is cheap to ship). Tell them you are looking for a thwart for an XXXX year avon raft. The serial number on the raft should tell you what year the boat is.
Avon might be able to sell you one, but that depends, Googler Avon rafts for their contact info.