You can easily fabricate that one. You just need some steel stock about 1/8” thick and an inch wide. Cut the plate, drill two holes to fit the bumper holes and then hold it in place and line up the little tab. If you don't weld, a muffler shop would probably do it for you.
BTW, these bumpers are completely adjustable can be aligned perfectly if you take the time and have patience. Drives me nuts to see otherwise nice Duettos with misaligned bumpers and crooked turn signals.
84 Spider Veloce
18 4C Spider