I got a set from ConceptzPerformance in the US.
http://www.conceptzperformance.com/Cart/description.php?II=1214&Car_Type=350Z&UID=20130509065421195.59.155.227
They worked out at about £55 delivered ($82.95 x 0.6 = £49.77 + Barclaycard foreign exchange = £55ish). They even put on the customs docket that they cost below the threshold for import duty, so was a bit of a result, but even with tax and royal mail handling it works out cheaper than anywhere I found in the UK... just.