I bought some new from Rimmers&Bros last year.
Apperently they no longer have them:
Trim - Centre Alloy Wheel - Silver Sparkle - 142mm Sports Style 6 - Plastic - Straights - RRJ000051MNH - Genuine MG Rover 
From SN-From 3D274575, CP Type-VIN, Qty Req-4, Application-MG ZT & ZT-T
RRJ000051MNH
No longer available