Spotted these on eBay but by the looks of it he has only the RHS front and back covers,but it might worth emailing him if he has or can get the LHS covers.
Not sure if that is the going rate for the leather hoop covers.
http://cgi.ebay.co.uk/BMW-Z4-ROLL-OVER-BAR-LEATHER-COVER-GENUINE-51438040426-/330457546360?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4cf0cdfe78
Not sure if that is the going rate for the leather hoop covers.
http://cgi.ebay.co.uk/BMW-Z4-ROLL-OVER-BAR-LEATHER-COVER-GENUINE-51438040426-/330457546360?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4cf0cdfe78