I wonder if you could use a small magnet (like one of those telescoping ones)
that could fit inside the combustion chamber  to fish around for it.  Of
course it could be embedded into the piston somewhere or could have gone out
the exhaust valve as well.  I am not saying this for sure but most likely a
piece that small probably just got pushed out the exhaust and hopefully didn't
hurt anything.  The only real way to tell is to pull the head and take a look.
Have fun.
Ken Wilford
John 3:16