As you are in South Wales you have Umfaan who is over on the Z4Forum and breaks Z4's, he may be able to help you source a replacement, located near Bridgend. Join Z4Forum and post on there your needs, he will no doubt see it and reply.
We have an enthusiasts Whats App Group across South Wales 'Zedshed Cymru' which we keep in touch with and cater for Z3 and Z4's, usually use my home garage as a Zedshed to do work on our cars when required, full diagnostics etc. If you want to join in just send me a PM on here with phone number and exact model of car and your location and I will add you in. Currently over 50 members across South Wales and some Bristol and Gloucester members.
Whilst you are at it update your user details on this forum so your location and exact car model you have, it assists us answering questions you ask and save you typing them in each time.
Umfaan (Barry) is on our Whats App Group as well.