The amp comes with these plugs:
https://images.sonicelectronix.com/i...g/xmgs6dsp.jpg
If you bought your amp used then ask the seller for them.
If the seller doesn't have them then you can try to contact Sony support and buy them direct from Sony?
EDIT: If you do have to buy these and can buy them piece by piece then don't bother with the "High-Level Input" harness as that one won't be needed. You'll need the other two