I don't think it is possible to do that in any standard way. There are converters for Amiga to use PC keyboard, but not the other way round.
What you could do; but it's not an easy solution is to use an Amiga 1200 keyboard, connect it to a Keyrah and place it in an A2000 keyboards casing. That will give you an USB keyboard you can use on your PC, but no PS/2 unfortunatly