The most informed 928 guy in the country is Paul Anderson who is based in Stroud, must be worth popping over to him from South Wales 07816 668088 or email to enquiries@928spares.co.uk
There is a specialist in Penarth who trades as RS Porsche, The owner is an ex Porsche Head Mechanic, I have not used him myself but have only heard good reports and he does seem to have a lot of the older models outside, and has been trading for quite a few years.