welcome! I'm not sure where you can get just that part off of a seat... without purchasing the entire seat! The 1999-2006 tigers had 2 of them - the pillion seat has it on the seat itself, while the front seat has it as a bolt on the frame (the seat has the latch that you already have, or a version of it anyway). The bolt version for the front seat is around $18, and there is a rubber spacer that is a few more dollars I think.
I never figured out how to mount that to the seat. Might be able to fabricate a bracket and attach the bracket to the seat pan itself. interesting idea though.