I ordered "part number PAS9021-25 description Seat Back Panel Retainers Ford"
They are shorter than the original darts but they are the right size for the holes in the boat. The problem is that the head that goes in the seat is not exactly the right size so you have to get creative and trim it so that it fits, but not too loosely so that the seat pops right off.
They are like $5.99 for 25 darts so it was worth a try. Good luck!