FT 204 sounds like a Wilmott Breeden key number?...... Try a classic car spares company or fleabay..... Just checked fleabay at least one FT 204 for sale .
Also any key cutter should be able to produce one via their computer.
Good luck!

1969 4/4
1995 plus 8
2002 Aero S1
2013 M3W
2014 Plus 8