Get a magnet on a stick and see if you get lucky and find the piece first if nothing else is wrong with the ratchet. Kit will take a few days to arrive so it might be worth wasting 10 minutes first.
It's hard to tell without the rest of the parts there to see orientation but if that's the internal selector I'd imagine it's just a pin, springs and bearings would be in the actually pawl assembly. Could be wrong though, haven't disassembled a 1/4 beyond just pulling the head out for degunking and inspection.