This company sells most of the BMW connectors and alot of older Rover ones http://www.simtekuk.co.uk/
. If you click on 'Automotive connectors' on the left menu and then click on 'Multilock 070 series' it will come up with them. The HK amp uses the MALE 12 pin and the MALE 18 pin ones. The 12 pin one can be removed from any Rover/MG 25/45/TF or the later 200/400/MG-F with the Lucas 5AS alarm. The white plug is the same. You will have to cut both connectors off the other car to have enough pins for the Lucas 5as way as they only use 4 or 5 and the HK needs all 12. If you buy them from this company you do get the pins but you need a special crimp tool to crimp the wires.
I do have the tool if anybody needs to borrow it.